What does the Milky Way weigh? Hubble and Gaia investigate

 

Cosmos by John Hussey

 

We can’t put the whole Milky Way on a scale, but astronomers have been able to come up with one of the most accurate measurements yet of our galaxy’s mass, using NASA’s Hubble Space Telescope and the European Space Agency’s Gaia satellite.

This illustration shows the fundamental architecture of our island city of stars, the Milky Way galaxy: a spiral disk, central bulge, and diffuse halo of stars and globular star clusters. Not shown is the vast halo of dark matter surrounding our galaxy. Credit: NASA, ESA and A. Feild (STScI)  

 

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We can’t put the whole Milky Way on a scale, but astronomers have been able to come up with one of the most accurate measurements yet of our galaxy’s mass, using NASA’s Hubble Space Telescope and the European Space Agency’s Gaia satellite.   The Milky Way weighs in at about 1.5 trillion solar masses (one solar mass is the mass of our Sun), according to the latest measurements. Only a few percent of this is contributed by the approximately 200 billion stars in the Milky Way and includes a 4-million-solar-mass supermassive black hole at the center.

Most of the rest of the mass is locked up in dark matter, an invisible and mysterious substance that acts like scaffolding throughout the universe and keeps the stars in their galaxies.   Earlier research dating back several decades used a variety of observational techniques that provided estimates for our galaxy’s mass ranging between 500 billion to 3 trillion solar masses. The improved measurement is near the middle of this range.  

“We want to know the mass of the Milky Way more accurately so that we can put it into a cosmological context and compare it to simulations of galaxies in the evolving universe,” said Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. “Not knowing the precise mass of the Milky Way presents a problem for a lot of cosmological questions.”   The new mass estimate puts our galaxy on the beefier side, compared to other galaxies in the universe. The lightest galaxies are around a billion solar masses, while the heaviest are 30 trillion, or 30,000 times more massive. The Milky Way’s mass of 1.5 trillion solar masses is fairly normal for a galaxy of its brightness.  

Astronomers used Hubble and Gaia to measure the three-dimensional movement of globular star clusters — isolated spherical islands each containing hundreds of thousands of stars each that orbit the center of our galaxy.   Although we cannot see it, dark matter is the dominant form of matter in the universe, and it can be weighed through its influence on visible objects like the globular clusters.

The more massive a galaxy, the faster its globular clusters move under the pull of gravity. Most previous measurements have been along the line of sight to globular clusters, so astronomers know the speed at which a globular cluster is approaching or receding from Earth. However, Hubble and Gaia record the sideways motion of the globular clusters, from which a more reliable speed (and therefore gravitational acceleration) can be calculated.  

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  The Hubble and Gaia observations are complementary. Gaia was exclusively designed to create a precise three-dimensional map of astronomical objects throughout the Milky Way and track their motions. It made exacting all-sky measurements that include many globular clusters. Hubble has a smaller field of view, but it can measure fainter stars and therefore reach more distant clusters. The new study augmented Gaia measurements for 34 globular clusters out to 65,000 light-years, with Hubble measurements of 12 clusters out to 130,000 light-years that were obtained from images taken over a 10-year period.  

When the Gaia and Hubble measurements are combined as anchor points, like pins on a map, astronomers can estimate the distribution of the Milky Way’s mass out to nearly 1 million light-years from Earth.   “We know from cosmological simulations what the distribution of mass in the galaxies should look like, so we can calculate how accurate this extrapolation is for the Milky Way,” said Laura Watkins of the European Southern Observatory in Garching, Germany, lead author of the combined Hubble and Gaia study, to be published in The Astrophysical Journal.

These calculations based on the precise measurements of globular cluster motion from Gaia and Hubble enabled the researchers to pin down the mass of the entire Milky Way.   The earliest homesteaders of the Milky Way, globular clusters contain the oldest known stars, dating back to a few hundred million years after the big bang, the event that created the universe. They formed prior to the construction of the Milky Way’s spiral disk, where our Sun and solar system reside.   “Because of their great distances, globular star clusters are some of the best tracers astronomers have to measure the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk of stars,” said Tony Sohn of STScI, who led the Hubble measurements.  

The international team of astronomers in this study are Laura Watkins (European Southern Observatory, Garching, Germany), Roeland van der Marel (Space Telescope Science Institute, and Johns Hopkins University Center for Astrophysical Sciences, Baltimore, Maryland), Sangmo Tony Sohn (Space Telescope Science Institute, Baltimore, Maryland), and N. Wyn Evans (University of Cambridge, Cambridge, United Kingdom).  

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.  

Story Source:  

Materials provided by NASA/Goddard Space Flight Center.  

Cosmos by John Hussey  

https://www.sciencedaily.com/releases/2019/03/190307131412.htm  

 

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Making the Hubble’s deepest images even deeper

 

Cosmos by John Hussey

It has taken researchers almost three years to produce the deepest image of the Universe ever taken from space, by recovering a large quantity of ‘lost’ light around the largest galaxies in the Hubble Ultra-Deep Field.

The new version of Hubble’s deep image. In dark grey you can see the new light that has been found around the galaxies in this field. That light corresponds to the brightness of more than one hundred billion suns.

Credit: A. S. Borlaff et al.

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  To produce the deepest image of the Universe from space a group of researchers from the Instituto de Astrofísica de Canarias (IAC) led by Alejandro S. Borlaff used original images from the Hubble Space Telescope (HST taken over a region in the sky called the Hubble Ultra-Deep Field (HUDF). After improving the process of combining several images the group was able to recover a large quantity of light from the outer zones of the largest galaxies in the HUDF. Recovering this light, emitted by the stars in these outer zones, was equivalent to recovering the light from a complete galaxy (“smeared out” over the whole field) and for some galaxies this missing light shows that they have diameters almost twice as big as previously measured.  

The HUDF is the result of combining hundreds of images taken with the Wide Field Camera 3 (WFC3) of the HST during over 230 hours of observation which, in 2012, yielded the deepest image of the Universe taken until then. But the method of combining the individual images was not ideally suited to detect faint extended objects. To do this, Borlaff explains “What we have done is to go back to the archive of the original images, directly as observed by the HST, and improve the process of combination, aiming at the best image quality not only for the more distant smaller galaxies but also for the extended regions of the largest galaxies.

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The WFC3 with which the data were taken was installed by astronauts in May 2009, when the Hubble had already been in space for 19 years. This was a major challenge for the researchers because the complete instrument (telescope+ camera) could not be tested on the ground, which made calibration more difficult. To overcome the problems they analysed several thousand images of different regions on the sky, with the aim of improving the calibration of the telescope on orbit.  

The image of the universe which is now the deepest “has been possible thanks to a striking improvement in the techniques of image processing which has been achieved in recent years, a field in which the group working in the IAC is at the forefront,” says Borlaff.  

 

Story Source:   Materials provided by Instituto de Astrofísica de Canarias (IAC).  

 

Cosmos by John Hussey  

 

https://www.sciencedaily.com/releases/2019/01/190124084812.htm  

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Milky Way’s neighbors pick up the pace

 

Cosmos by John Hussey

After slowly forming stars for the first few billion years of their lives, the Magellanic Clouds, near neighbors of our own Milky Way galaxy, have upped their game and are now forming new stars at a fast clip. This new insight into the history of the Clouds comes from the first detailed chemical maps made of galaxies beyond the Milky Way.

Taken with the European Southern Observatory’s Gaia Satellite, the maps show the relative abundance of heavy elements (elements heavier than helium) in the stars. Yellow indicates fewer heavy elements and purple indicates more heavy elements. Credit: David Nidever (NOAO/Montana State University) and the SDSS collaboration.

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After slowly forming stars for the first few billion years of their lives, the Magellanic Clouds, near neighbors of our own Milky Way galaxy, have upped their game and are now forming new stars at a fast clip. This new insight into the history of the Clouds comes from the first detailed chemical maps made of galaxies beyond the Milky Way. Named for explorer Ferdinand Magellan, who led the first European expedition to circumnavigate the globe, the Large and Small Magellanic Clouds are the Milky Way’s nearest galactic neighbors — companion galaxies that will someday merge with our galaxy. The two galaxies are visible only from the Southern Hemisphere, where they look like bright, wispy clouds.  

 

A Map to Stellar History

Although humans have gazed at the Clouds for millennia, this is the first time astronomers have made a detailed map of the chemical compositions of the stars within them. The project, carried out by the Sloan Digital Sky Survey (SDSS), was led by NOAO astronomer David Nidever, who is also a research professor of physics at Montana State University. “We mapped the positions, movements, and chemical make-up of thousands of stars in the Magellanic Clouds,” said Nidever. “Reading these maps helps us reconstruct the history of when these galaxies formed their stars.” The maps are the first major discovery to come out of the new southern operations of SDSS’s Apache Point Observatory Galaxy Evolution Experiment 2 (APOGEE-2) survey, which is being carried out on the Irénée du Pont Telescope at Las Campanas Observatory in Chile.

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Making Maps from Stellar Spectra

To make the maps, the SDSS team collected spectra of as many stars as possible. Spectra, which spread out the light from a star in the form of a rainbow, encode the motions of stars, their temperature, the chemical elements they contain, and their stage in the stellar life cycle. By measuring the chemical make-up of a galaxy’s stars, astronomers are able to infer their “star formation history,” a rough record of the rate at which stars formed over time. The reconstruction is possible because of the difference in the lifetimes of stars of different masses and the role more massive stars play in enriching galaxies with heavy elements.

As stars age, stars more massive than the Sun evolve and explode as supernovae, ejecting heavy elements out into the galaxy, while less massive stars live on. The ejected elements mix with the existing gas, enriching it. New generations of stars form from the enriched gas and inherit that chemical make-up. The process repeats, with the longer-lived lower mass stars surviving to record the enrichment history of the galaxy. By mapping the abundances of these stars, astronomers can “read” the star formation record of the galaxy.  

 

Slow Start Followed by a Bang

The results show that the star formation history of the Large and Small Magellanic Clouds is completely different from that of our galaxy. “In the Milky Way, star formation began like gangbusters and later declined,” explained team member Sten Hasselquist from the University of Utah. “In contrast, in the Magellanic Clouds, stars formed extremely slowly at early times, at a rate only 1/50th of the star formation rate in the Milky Way, but that rate has skyrocketed in the last 2 billion years.” Nidever thinks that the dramatic increase in the star formation rate is due to the interaction of the Magellanic Clouds with one another as they tumble toward the Milky Way.

“The Clouds began their lives calmly in a relatively isolated part of the Universe, where there was no reason to form stars,” said Nidever. “But in the last few billion years, the close interactions that the Clouds have had with each other and with the Milky Way is causing the gas in the Clouds to transform into stars.”  

 

Fireworks Ahead!

Over the next several billion years, the Magellanic Clouds will continue to merge with the Milky Way, as the gravitational force of the much more massive Milky Way pulls them in. As the merger progresses, star formation in the Clouds is expected to reach an even greater, fevered pitch, according to recent work. In about 2.5 billion years, the Large Magellanic Cloud will be entirely consumed by the Milky Way in a cosmic explosion of star formation. Our nearest neighbors may have gotten off to a slow start, but exciting times lie ahead!  

Story Source:

Materials provided by Association of Universities for Research in Astronomy (AURA).  

 

Cosmos by John Hussey  

 

https://www.sciencedaily.com/releases/2019/01/190122115037.htm  

 

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Did supernovae kill off large ocean animals at dawn of Pleistocene?

 

Cosmos by John Hussey

The effects of a supernova — and possibly more than one — on large ocean life like school-bus-sized Megalodon 2.6 million years ago are detailed in a new article.

A nearby supernova remnant. Credit: NASA

 

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About 2.6 million years ago, an oddly bright light arrived in the prehistoric sky and lingered there for weeks or months. It was a supernova some 150 light years away from Earth. Within a few hundred years, long after the strange light in the sky had dwindled, a tsunami of cosmic energy from that same shattering star explosion could have reached our planet and pummeled the atmosphere, touching off climate change and triggering mass extinctions of large ocean animals, including a shark species that was the size of a school bus.

The effects of such a supernova — and possibly more than one — on large ocean life are detailed in a paper just published in Astrobiology. “I’ve been doing research like this for about 15 years, and always in the past it’s been based on what we know generally about the universe — that these supernovae should have affected Earth at some time or another,” said lead author Adrian Melott, professor emeritus of physics & astronomy at the University of Kansas.

“This time, it’s different. We have evidence of nearby events at a specific time. We know about how far away they were, so we can actually compute how that would have affected the Earth and compare it to what we know about what happened at that time — it’s much more specific.” Melott said recent papers revealing ancient seabed deposits of iron-60 isotopes provided the “slam-dunk” evidence of the timing and distance of supernovae.

“As far back as the mid-1990s, people said, ‘Hey, look for iron-60. It’s a telltale because there’s no other way for it to get to Earth but from a supernova.’ Because iron-60 is radioactive, if it was formed with the Earth it would be long gone by now. So, it had to have been rained down on us. There’s some debate about whether there was only one supernova really nearby or a whole chain of them. I kind of favor a combo of the two — a big chain with one that was unusually powerful and close.

If you look at iron-60 residue, there’s a huge spike 2.6 million years ago, but there’s excess scattered clear back 10 million years.” Melott’s co-authors were Franciole Marinho of Universidade Federal de Sa?o Carlos in Brazil and Laura Paulucci of Universidade Federal do ABC, also in Brazil. According to the team, other evidence for a series of supernovae is found in the very architecture of the local universe. “We have the Local Bubble in the interstellar medium,” Melott said. “We’re right on its edge.

It’s a giant region about 300 light years long. It’s basically very hot, very low-density gas — nearly all the gas clouds have been swept out of it. The best way to manufacture a bubble like that is a whole bunch of supernovae blows it bigger and bigger, and that seems to fit well with idea of a chain.

When we do calculations, they’re based on the idea that one supernova that goes off, and its energy sweeps by Earth, and it’s over. But with the Local Bubble, the cosmic rays kind of bounce off the sides, and the cosmic-ray bath would last 10,000 to 100,000 years. This way, you could imagine a whole series of these things feeding more and more cosmic rays into the Local Bubble and giving us cosmic rays for millions of years.

” Whether or not there was one supernova or a series of them, the supernova energy that spread layers of iron-60 all over the world also caused penetrating particles called muons to shower Earth, causing cancers and mutations — especially to larger animals.

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“The best description of a muon would be a very heavy electron — but a muon is a couple hundred times more massive than an electron,” Melott said. “They’re very penetrating. Even normally, there are lots of them passing through us.

Nearly all of them pass through harmlessly, yet about one-fifth of our radiation dose comes by muons. But when this wave of cosmic rays hits, multiply those muons by a few hundred. Only a small faction of them will interact in any way, but when the number is so large and their energy so high, you get increased mutations and cancer — these would be the main biological effects.

We estimated the cancer rate would go up about 50 percent for something the size of a human — and the bigger you are, the worse it is. For an elephant or a whale, the radiation dose goes way up.” A supernova 2.6 million years ago may be related to a marine megafaunal extinction at the Pliocene-Pleistocene boundary where 36 percent of the genera were estimated to become extinct.

The extinction was concentrated in coastal waters, where larger organisms would catch a greater radiation dose from the muons. According to the authors of the new paper, damage from muons would extend down hundreds of yards into ocean waters, becoming less severe at greater depths: “High energy muons can reach deeper in the oceans being the more relevant agent of biological damage as depth increases,” they write. Indeed, a famously large and fierce marine animal inhabiting shallower waters may have been doomed by the supernova radiation.

“One of the extinctions that happened 2.6 million years ago was Megalodon,” Melott said. “Imagine the Great White Shark in ‘Jaws,’ which was enormous — and that’s Megalodon, but it was about the size of a school bus. They just disappeared about that time. So, we can speculate it might have something to do with the muons. Basically, the bigger the creature is the bigger the increase in radiation would have been.” The KU researcher said the evidence of a supernova, or series of them, is “another puzzle piece” to clarify the possible reasons for the Pliocene-Pleistocene boundary extinction.

“There really hasn’t been any good explanation for the marine megafaunal extinction,” Melott said. “This could be one. It’s this paradigm change — we know something happened and when it happened, so for the first time we can really dig in and look for things in a definite way. We now can get really definite about what the effects of radiation would be in a way that wasn’t possible before.”  

 

Story Source:

Materials provided by University of Kansas.  

 

Cosmos by John Hussey  

https://www.sciencedaily.com/releases/2018/12/181211112941.htm

 

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Tangled magnetic fields power cosmic particle accelerators

 

Cosmos by John Hussey

New way to explain how a black hole’s plasma jets boost particles to the highest energies observed in the universe Magnetic field lines tangled like spaghetti in a bowl might be behind the most powerful particle accelerators in the universe. That’s the result of a new computational study that simulated particle emissions from distant active galaxies. SLAC researchers have found a new mechanism that could explain how plasma jets emerging from the center of active galaxies, like the one shown in this illustration, accelerate particles to extreme energies. Computer simulations (circled area) showed that tangled magnetic field lines create strong electric fields in the direction of the jets, leading to dense electric currents of high-energy particles streaming away from the galaxy. Credit: Greg Stewart/SLAC National Accelerator Laboratory

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Magnetic field lines tangled like spaghetti in a bowl might be behind the most powerful particle accelerators in the universe. That’s the result of a new computational study by researchers from the Department of Energy’s SLAC National Accelerator Laboratory, which simulated particle emissions from distant active galaxies. At the core of these active galaxies, supermassive black holes launch high-speed jets of plasma — a hot, ionized gas — that shoot millions of light years into space. This process may be the source of cosmic rays with energies tens of millions of times higher than the energy unleashed in the most powerful human-made particle accelerator. “The mechanism that creates these extreme particle energies isn’t known yet,” said SLAC staff scientist Frederico Fiúza, the principal investigator of a new study that will publish tomorrow in Physical Review Letters. “But based on our simulations, we’re able to propose a new mechanism that can potentially explain how these cosmic particle accelerators work.” The results could also have implications for plasma and nuclear fusion research and the development of novel high-energy particle accelerators. Simulating cosmic jets Researchers have long been fascinated by the violent processes that boost the energy of cosmic particles. For example, they’ve gathered evidence that shock waves from powerful star explosions could bring particles up to speed and send them across the universe. Scientists have also suggested that the main driving force for cosmic plasma jets could be magnetic energy released when magnetic field lines in plasmas break and reconnect in a different way — a process known as “magnetic reconnection.”

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However, the new study suggests a different mechanism that’s tied to the disruption of the helical magnetic field generated by the supermassive black hole spinning at the center of active galaxies. “We knew that these fields can become unstable,” said lead author Paulo Alves, a research associate working with Fiúza. “But what exactly happens when the magnetic fields become distorted, and could this process explain how particles gain tremendous energy in these jets? That’s what we wanted to find out in our study.” To do so, the researchers simulated the motions of up to 550 billion particles — a miniature version of a cosmic jet — on the Mira supercomputer at the Argonne Leadership Computing Facility (ALCF) at DOE’s Argonne National Laboratory. Then, they scaled up their results to cosmic dimensions and compared them to astrophysical observations. From tangled field lines to high-energy particles The simulations showed that when the helical magnetic field is strongly distorted, the magnetic field lines become highly tangled and a large electric field is produced inside the jet. This arrangement of electric and magnetic fields can, indeed, efficiently accelerate electrons and protons to extreme energies. While high-energy electrons radiate their energy away in the form of X-rays and gamma rays, protons can escape the jet into space and reach Earth’s atmosphere as cosmic radiation. “We see that a large portion of the magnetic energy released in the process goes into high-energy particles, and the acceleration mechanism can explain both the high-energy radiation coming from active galaxies and the highest cosmic-ray energies observed,” Alves said. Roger Blandford, an expert in black hole physics and former director of the SLAC/Stanford University Kavli Institute for Particle Astrophysics and Cosmology (KIPAC), who was not involved in the study, said, “This careful analysis identifies many surprising details of what happens under conditions thought to be present in distant jets, and may help explain some remarkable astrophysical observations.” Next, the researchers want to connect their work even more firmly with actual observations, for example by studying what makes the radiation from cosmic jets vary rapidly over time. They also intend to do lab research to determine if the same mechanism proposed in this study could also cause disruptions and particle acceleration in fusion plasmas. This work was also co-authored by Jonathan Zrake, a former Kavli Fellow at KIPAC, who is now at Columbia University. The project was supported by the DOE Office of Science through its Early Career Research Program and an ALCC award for simulations on the Mira high-performance computer. ALCF is a DOE Office of Science user facility.   Story Source: Materials provided by DOE/SLAC National Accelerator Laboratory. Original written by Manuel Gnida.   Cosmos by John Hussey   https://www.sciencedaily.com/releases/2018/12/181213131242.htm  

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Calibrating cosmic mile markers

 

Cosmos by John Hussey

New work provides the best-yet calibrations for using type Ia supernovae to measure cosmic distances, which has implications for our understanding of how fast the universe is expanding and the role dark energy may play in driving this process.. An artist’s conception of what’s called the cosmic distance ladder — a series of celestial objects, including type Ia supernovae that have known distances and can be used to calculate the rate at which the universe is expanding. Credit: NASA/JPL-Caltech

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New work from the Carnegie Supernova Project provides the best-yet calibrations for using type Ia supernovae to measure cosmic distances, which has implications for our understanding of how fast the universe is expanding and the role dark energy may play in driving this process. Led by Carnegie astronomer Chris Burns, the team’s findings are published in The Astrophysical Journal. Type Ia supernovae are fantastically bright stellar phenomena. They are violent explosions of a white dwarf — the crystalline remnant of a star that has exhausted its nuclear fuel — which is part of a binary system with another star. In addition to being exciting to observe in their own right, type Ia supernovae are also a vital tool that astronomers use as a kind of cosmic mile marker to infer the distances of celestial objects. While the precise details of the explosion are still unknown, it is believed that they are triggered when the white dwarf approaches a critical mass, so the brightness of the phenomenon is predictable from the energy of the explosion. The difference between the predicted brightness and the brightness observed from Earth tells us the distance to the supernova. Astronomers employ these precise distance measurements, along with the speed at which their host galaxies are receding, to determine the rate at which the universe is expanding. Thanks to the finite speed of light, not only can we measure how quickly the universe is expanding right now, but by looking farther and farther out into space, we see further back in time and can measure how fast the universe was expanding in the distant past. This led to the astonishing discovery in the late-1990s that the universe’s expansion is currently speeding up due to the repulsive effect of a mysterious “dark” energy. Improving the distance estimates made using type Ia supernovae will help astronomers better understand the role that dark energy plays in this cosmic expansion. “Beginning with its namesake, Edwin Hubble, Carnegie astronomers have a long history of working on the Hubble constant, including vital contributions to our understanding of the universe’s expansion made by Alan Sandage and Wendy Freedman,” said Observatories Director John Mulchaey. However, the speed at which the brightness of type Ia supernova explosions fade away is not uniform. In 1993, Carnegie astronomer Mark Phillips showed that the explosions that take longer to fade away are intrinsically brighter than those that fade away quickly. This correlation, which is commonly referred to as the Phillips relation, allowed a group of astronomers in Chile, includingPhillips and Texas A&M astronomer Nicholas Suntzeff, to develop type Ia supernovae into a precise tool for measuring the expansion of the universe.

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Studying the supernovae using the near-infrared part of the spectrum was crucial to this finding. The light from these explosions must travel through cosmic dust to reach our telescopes, and these fine-grained interstellar particles obscure light on the blue end of the spectrum more than they do light from the red end of the spectrum in the same manner as smoke from a forest fire makes everything appear redder. This can trick astronomers into thinking that a supernova is farther away than it is. But working in the infrared allows astronomers to peer more clearly through this dusty veil. “One of the Carnegie Supernova Project’s primary goals has been to provide a reliable, high-quality sample of supernovae and dependable methods for inferring their distances,” said lead author Burns. “The quality of this data allows us to better correct our measurements to account for the dimming effect of cosmic dust” added Mark Phillips, an astronomer at Carnegie’s Las Campanas Observatory in Chile and a co-author on the paper. The calibration of these mile markers is crucially important, because there are disagreements between different methods for determining the universe’s expansion rate. The Hubble constant can independently be estimated using the glow of background radiation left over from the Big Bang. This cosmic microwave background radiation has been measured with exquisite detail by the Planck satellite, and it gives astronomers a more slowly expanding universe than when measured using type Ia supernovae. “This discrepancy could herald new physics, but only if it’s real,” Burns explained. “So, we need our type Ia supernova measurements to be as accurate as possible, but also to identify and quantify all sources of error.” The Carnegie Supernova Project is supported by the U.S. National Science Foundation. Computing resources for this work were made possible by the Ahmanson Foundation. The Cynthia and George Mitchell Foundation and Sheridan Lorenz supported several CSP workshops.   Story Source: Materials provided by Carnegie Institution for Science.   Cosmos by John Hussey   https://www.sciencedaily.com/releases/2018/11/181129110147.htm  

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Bringing balance to the universe: New theory could explain missing 95 percent of the cosmos

 

Cosmos by John Hussey

New research could shed light on the ‘missing’ dark matter and dark energy that make up 95 percent of our universe and yet are wholly invisible to us. Milky Way (stock image). Credit: © mandritoiu / Fotolia

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Scientists at the University of Oxford may have solved one of the biggest questions in modern physics, with a new paper unifying dark matter and dark energy into a single phenomenon: a fluid which possesses ‘negative mass’. If you were to push a negative mass, it would accelerate towards you. This astonishing new theory may also prove right a prediction that Einstein made 100 years ago. Our current, widely recognised model of the Universe, called LambdaCDM, tells us nothing about what dark matter and dark energy are like physically. We only know about them because of the gravitational effects they have on other, observable matter. This new model, published today in Astronomy and Astrophysics, by Dr Jamie Farnes from the Oxford e-Research Centre, Department of Engineering Science, offers a new explanation. Dr Farnes says: “We now think that both dark matter and dark energy can be unified into a fluid which possesses a type of ‘negative gravity’, repelling all other material around them. Although this matter is peculiar to us, it suggests that our cosmos is symmetrical in both positive and negative qualities.” The existence of negative matter had previously been ruled out as it was thought this material would become less dense as the Universe expands, which runs contrary to our observations that show dark energy does not thin out over time. However, Dr Farnes’ research applies a ‘creation tensor’, which allows for negative masses to be continuously created. It demonstrates that when more and more negative masses are continually bursting into existence, this negative mass fluid does not dilute during the expansion of the cosmos. In fact, the fluid appears to be identical to dark energy.

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Dr Farnes’s theory also provides the first correct predictions of the behaviour of dark matter halos. Most galaxies are rotating so rapidly they should be tearing themselves apart, which suggests that an invisible ‘halo’ of dark matter must be holding them together. The new research published today features a computer simulation of the properties of negative mass, which predicts the formation of dark matter halos just like the ones inferred by observations using modern radio telescopes.   Albert Einstein provided the first hint of the dark universe exactly 100 years ago, when he discovered a parameter in his equations known as the ‘cosmological constant’, which we now know to be synonymous with dark energy. Einstein famously called the cosmological constant his ‘biggest blunder’, although modern astrophysical observations prove that it is a real phenomenon. In notes dating back to 1918, Einstein described his cosmological constant, writing that “a modification of the theory is required such that ’empty space’ takes the role of gravitating negative masses which are distributed all over the interstellar space.” It is therefore possible that Einstein himself predicted a negative-mass-filled universe.   Dr Farnes says: “Previous approaches to combining dark energy and dark matter have attempted to modify Einstein’s theory of general relativity, which has turned out to be incredibly challenging. This new approach takes two old ideas that are known to be compatible with Einstein’s theory — negative masses and matter creation — and combines them together.   “The outcome seems rather beautiful: dark energy and dark matter can be unified into a single substance, with both effects being simply explainable as positive mass matter surfing on a sea of negative masses.”   Proof of Dr Farnes’s theory will come from tests performed with a cutting-edge radio telescope known as the Square Kilometre Array (SKA), an international endeavour to build the world’s largest telescope in which the University of Oxford is collaborating.   Dr Farnes adds: “There are still many theoretical issues and computational simulations to work through, and LambdaCDM has a nearly 30 year head start, but I’m looking forward to seeing whether this new extended version of LambdaCDM can accurately match other observational evidence of our cosmology. If real, it would suggest that the missing 95% of the cosmos had an aesthetic solution: we had forgotten to include a simple minus sign.”   Story Source:   Materials provided by University of Oxford.   Cosmos by John Hussey   https://www.sciencedaily.com/releases/2018/11/181129110147.htm  

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Macroscopic phenomena governed by microscopic physics

 

Cosmos by John Hussey

Researchers have observed a magnetic reconnection driven by electron dynamics in laser-produced plasmas. Magnetic reconnections are often observed in the magnetic flux on the Sun and the Earth’s magnetosphere. It has been highly challenging to reveal the electron scale, microscopic information in the vast universe. Applying a weak magnetic field, where only electrons are directly coupled with the magnetic field, we observed a plasmoid and cusp-like features typical to magnetic reconnections. Imaging of plasma emission shows the plasmoid and cusp-like features typical of magnetic reconnections. Credit: Osaka University

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It has been difficult to simultaneously obtain micro- and macroscopic information in outer space. Global images of distant astrophysical phenomena provide macroscopic information; however, local information is inaccessible. In contrast, in situ observations with spacecrafts provide microscopic information of phenomena such as the Earth’s magnetosphere, but it is difficult to obtain global information in near space. In the so-called “laboratory astrophysics,” a relatively new field born at Osaka University that has been adopted and developed all over the world, space and astrophysical phenomena are experimentally investigated. A research group led by Yasuhiro Kuramitsu at Osaka University has revealed a magnetic reconnection driven by electron dynamics for the first time ever in laser-produced plasmas using the Gekko XII laser facility at the Institute of Laser Engineering, Osaka University. Magnetic reconnection is an essential factor in the universe, where the anti-parallel components of magnetic fields re-connect and release magnetic energy as plasma kinetic energy. Electron dynamics is considered to be essential in the triggering process of magnetic reconnection; however, it has been highly challenging to observe electron-scale, microscopic information together with the macroscopic reconnection structure in outer space.

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The research group applied a weak magnetic field to the laser-produced plasma so that only electrons are directly coupled with the magnetic field. Plasma collimation was observed with interferometry only when the magnetic field was applied, i.e., the magnetic field was distorted by the plasma pressure and local anti-parallel. By further applying external pressure with an ambient plasma, a plasmoid associated with cusp-like features was observed through imaging of plasma emissions. The plasmoid propagated at the Alfvén velocity defined with electron mass, indicating the magnetic reconnection driven by electron dynamics. The outcomes of this research will shed light on the role of electrons in laboratory plasmas. Since the spatio-temporal scales of electrons are much smaller than those of ions, it is highly challenging to resolve electron scale phenomena while imaging global structures of phenomena. This is also the case in outer space, as it has been difficult to obtain microscopic and macroscopic information simultaneously. In this study, the strength of the magnetic field is controlled to only allow electrons to couple with the magnetic field. This is a unique and powerful feature of laboratory experiment, and thus, laboratory astrophysics can be an alternative tool to investigate space and astrophysical phenomena. The roles of electron dynamics are essential not only to magnetic reconnection but also to various phenomena in the universe and in the laboratory, including fusion plasmas. Knowing more about the universe will lead to new technology in the future.   Story Source: Materials provided by Osaka University.   Cosmos by John Hussey   https://www.sciencedaily.com/releases/2018/11/181129110147.htm  

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All of the starlight ever produced by the observable universe measured

 

Cosmos by John Hussey

The team’s measurement, collected from Fermi data, has never been done before

From their laboratories on a rocky planet dwarfed by the vastness of space, scientists have collaborated to measure all of the starlight ever produced throughout the history of the observable universe.

This map of the entire sky shows the location of 739 blazars used in the Fermi Gamma-ray Space Telescope’s measurement of the extragalactic background light (EBL). The background shows the sky as it appears in gamma rays with energies above 10 billion electron volts, constructed from nine years of observations by Fermi’s Large Area Telescope. The plane of our Milky Way galaxy runs along the middle of the plot. Credit: NASA/DOE/Fermi LAT Collaboration

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From their laboratories on a rocky planet dwarfed by the vastness of space, Clemson University scientists have managed to measure all of the starlight ever produced throughout the history of the observable universe.

 

Astrophysicists believe that our universe, which is about 13.7 billion years old, began forming the first stars when it was a few hundred million years old. Since then, the universe has become a star-making tour de force. There are now about two trillion galaxies and a trillion-trillion stars. Using new methods of starlight measurement, Clemson College of Science astrophysicist Marco Ajello and his team analyzed data from NASA’s Fermi Gamma-ray Space Telescope to determine the history of star formation over most of the universe’s lifetime.

A collaborative paper titled “A gamma-ray determination of the Universe’s star-formation history” was published Nov. 30 in the journal Science and describes the results and ramifications of the team’s new measurement process.

“From data collected by the Fermi telescope, we were able to measure the entire amount of starlight ever emitted. This has never been done before,” said Ajello, who is lead author of the paper. “Most of this light is emitted by stars that live in galaxies. And so, this has allowed us to better understand the stellar-evolution process and gain captivating insights into how the universe produced its luminous content.”

Putting a number on the amount of starlight ever produced has several variables that make it difficult to quantify in simple terms. But according to the new measurement, the number of photons (particles of visible light) that escaped into space after being emitted by stars translates to 4×10^84.

Or put another way: 4,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 photons.

Despite this stupendously large number, it is interesting to note that with the exception of the light that comes from our own sun and galaxy, the rest of the starlight that reaches Earth is exceedingly dim — equivalent to a 60-watt light bulb viewed in complete darkness from about 2.5 miles away. This is because the universe is almost incomprehensibly huge. This is also why the sky is dark at night, other than light from the moon, visible stars and the faint glow of the Milky Way.

The Fermi Gamma-ray Space Telescope was launched into low orbit on June 11, 2008, and recently marked its 10-year anniversary. It is a powerful observatory that has provided enormous amounts of data on gamma rays (the most energetic form of light) and their interaction with the extragalactic background light (EBL), which is a cosmic fog composed of all the ultraviolet, visible and infrared light emitted by stars or from dust in their vicinity. Ajello and postdoctoral fellow Vaidehi Paliya analyzed almost nine years of data pertaining to gamma-ray signals from 739 blazars.

Blazars are galaxies containing supermassive black holes that are able to release narrowly collimated jets of energetic particles that leap out of their galaxies and streak across the cosmos at nearly the speed of light. When one of these jets happens to be pointed directly at Earth, it is detectable even when originating from extremely far away. Gamma ray photons produced within the jets eventually collide with the cosmic fog, leaving an observable imprint. This enabled Ajello’s team to measure the density of the fog not just at a given place but also at a given time in the history of the universe.

“Gamma-ray photons traveling through a fog of starlight have a large probability of being absorbed,” said Ajello, an assistant professor in the department of physics and astronomy. “By measuring how many photons have been absorbed, we were able to measure how thick the fog was and also measure, as a function of time, how much light there was in the entire range of wavelengths.”

Using galaxy surveys, the star-formation history of the universe has been studied for decades. But one obstacle faced by previous research was that some galaxies were too far away, or too faint, for any present-day telescopes to detect. This forced scientists to estimate the starlight produced by these distant galaxies rather than directly record it.


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Ajello’s team was able to circumvent this by using Fermi’s Large Area Telescope data to analyze the extragalactic background light. Starlight that escapes galaxies, including the most distant ones, eventually becomes part of the EBL. Therefore, accurate measurements of this cosmic fog, which have only recently become possible, eliminated the need to estimate light emissions from ultra-distant galaxies.

Paliya performed the gamma ray analysis of all 739 blazars, whose black holes are millions to billions of times more massive than our sun. “By using blazars at different distances from us, we measured the total starlight at different time periods,” said Paliya of the department of physics and astronomy. “We measured the total starlight of each epoch — one billion years ago, two billion years ago, six billion years ago, etc. — all the way back to when stars were first formed. This allowed us to reconstruct the EBL and determine the star-formation history of the universe in a more effective manner than had been achieved before.”

When high-energy gamma rays collide with low-energy visible light, they transform into pairs of electrons and positrons. According to NASA, Fermi’s ability to detect gamma rays across a wide range of energies makes it uniquely suited for mapping the cosmic fog.

These particle interactions occur over immense cosmic distances, which enabled Ajello’s group to probe deeper than ever into the universe’s star-forming productivity. “Scientists have tried to measure the EBL for a long time. However, very bright foregrounds like the zodiacal light (which is light scattered by dust in the solar system) rendered this measurement very challenging,” said co-author Abhishek Desai, a graduate research assistant in the department of physics and astronomy.

“Our technique is insensitive to any foreground and thus overcame these difficulties all at once.” Star formation, which occurs when dense regions of molecular clouds collapse and form stars, peaked around 11 billion years ago. But though the birthing of new stars has since slowed down, it has never stopped.

For instance, about seven new stars are created in our Milky Way galaxy every year. Establishing not only the present-day EBL, but revealing its evolution in cosmic history is a major breakthrough in this field, according to team member Dieter Hartmann, a professor in the department of physics and astronomy. “Star formation is a great cosmic cycling and recycling of energy, matter and metals.

It’s the motor of the universe,” Hartmann said. “Without the evolution of stars, we wouldn’t have the fundamental elements necessary for the existence of life.” Understanding star formation also has ramifications for other areas of astronomical study, including research regarding cosmic dust, galaxy evolution and dark matter.

The team’s analysis will provide future missions with a guideline to explore the earliest days of stellar evolution — such as the upcoming James Webb Space Telescope, which will be launched in 2021 and will enable scientists to hunt for the formation of primordial galaxies. “The first billion years of our universe’s history are a very interesting epoch that has not yet been probed by current satellites,” Ajello concluded.

“Our measurement allows us to peek inside it. Perhaps one day we will find a way to look all the way back to the Big Bang. This is our ultimate goal.”  

 

Story Source:

Materials provided by Clemson University.  

 

Cosmos by John Hussey  

 

https://www.sciencedaily.com/releases/2018/11/181129110147.htm  

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Gas clouds whirling around black hole form heart of distant astronomical object

 

Cosmos by John Hussey


First detailed observation of environs of a massive black hole outside Milky Way

Astronomers have concluded that gas clouds rapidly moving around a central black hole form the very heart of the 3C327 quasar, confirming earlier measurements.

Optical image of the quasar 3C 273 (the bright stellar-like object in the center) obtained with the Hubble Space Telescope. It was the first quasar ever to be identified.

Credit: NASA

In 1963, astronomer Maarten Schmidt identified the first quasi-stellar object or “quasar,” an extremely bright but distant object. He found the single quasar, the active nucleus of a far-away galaxy known to astronomers as 3C 273, to be 100 times more luminous than all the stars in our Milky Way combined.

Now, the GRAVITY international team of astronomers, including Prof. Hagai Netzer of Tel Aviv University’s School of Physics and Astronomy, have concluded that gas clouds rapidly moving around a central black hole form the very heart of this quasar. The results of the new research were published in Nature on November 29.

The first measurement of the mass of the black hole inside 3C 273, using an older method, was conducted at the TAU’s Florence and George Wise Observatory in 2000, as part of PhD research conducted by TAU’s Dr. Shai Kaspi, then a student in Prof. Netzer’s group. This result has now been corroborated by GRAVITY’s observations.

The research is the first detailed observation outside of our galaxy of gas clouds whirling around a central black hole. According to the researchers, GRAVITY’s measurements will become the benchmark for measuring black hole masses in thousands of other quasars.

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Taking a closer look at a black hole

The GRAVITY instrument, situated in Paranal, Chile, has unprecedented capabilities. It combines the collective area of four telescopes to form a virtual telescope, called an interferometer, 130 meters across. The instrument can detect distant astronomical objects at an extremely high resolution.

“Quasars are among the most distant astronomical objects that can be observed,” Prof. Netzer says. “They also play a fundamental role in the history of the universe, as their evolution is intricately tied to galaxy growth. While almost all large galaxies harbor a massive black hole at their centers, so far only one in our Milky Way has been accessible for such detailed studies.”

 

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“GRAVITY allowed us to resolve, for the first time ever, the motion of gas clouds around a central black hole,” says Eckhard Sturm of Max Planck Institute for Extraterrestrial Physics (MPE), who co-led the research for the study. “Our observations can follow the motion of the gas and reveal that the clouds do whirl around the central black hole.”

So far, such observations had not been possible due to the small angular size of a quasar’s inner region — roughly the size of our solar system, but some 2.5 billion light years distant from us.

“Broad emission lines created by gas in the vicinity of the black hole are observational hallmarks of quasars. Until now, the distance of the gas from the black hole, and occasionally the pattern of the motion, could only be measured by an older method that made use of light variations in the quasars,” Prof. Netzer says. “With the GRAVITY instrument, we can distinguish structures at the level of 10 micro-arc seconds, which corresponds to observing, for example, a 1-Euro coin on the Moon.”

“Information about the motion and distance of the gas immediately around the black hole is crucial to measuring the mass of the black hole,” explains Jason Dexter, also of MPE, who co-led the research. “For the first time, the old method was tested experimentally and passed its test with flying colors, confirming previous estimates of about 300 million solar masses for the black hole.”

“This is the first time that we can study the immediate environs of a massive black hole outside our home galaxy, the Milky Way,” concludes Reinhard Genzel, head of the infrared research group at MPE. “Black holes are intriguing objects, allowing us to probe physics under extreme conditions — and with GRAVITY we can now probe them both near and far.”

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Materials provided by American Friends of Tel Aviv University.

Cosmosby John Hussey

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