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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