Hawking Takes on the Infinite Multiverse

Cosmos by John Hussey


Stephen Hawking’s last paper on cosmology, published posthumously, might solve the problem of eternal inflation, a theory that suggests our cosmos is but one in a sea of infinite universes.

This symbolic representation shows the evolution of the universe over 13.7 billion years. The far left depicts the Big Bang, the earliest moment we can yet probe, when an extremely brief moment of “inflation” produced a burst of exponential growth in the universe. (Size is symbolized by the vertical extent in this graphic.)

NASA / WMAP

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Cosmic history

This symbolic representation shows the evolution of the universe over 13.7 billion years. The far left depicts the Big Bang, the earliest moment we can yet probe, when an extremely brief moment of “inflation” produced a burst of exponential growth in the universe. (Size is symbolized by the vertical extent in this graphic.)

There’s a lot of evidence to suggest that, just a tiny fraction of a second after the Big Bang, the infant universe went through a fantastic growth spurt. The phase itself lasted only a fraction of a second, but it’s responsible for the universe we see now. Even the particles that make up stars and humans alike were created from its energy.

The trouble is, according to most theories of cosmic inflation, the growth spurt never really stopped. Though our pocket of space, what we call our universe, might have stopped its exponential expansion, the overall universe never stopped stretching.

Now, in a paper published by Stephen Hawking (posthumously) and his colleague Thomas Hertog (KU Leuven, Belgium) in the Journal of High Energy Physics, the scientists turn that picture on its head, arguing that we need to rethink our universe’s beginnings. Applying quantum and string theory to a simplified mathematical model of the universe, Hawking and Hertog conclude that cosmic inflation isn’t eternal after all.

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Eternal Inflation

Why do most cosmologists think that inflation is eternal? The idea behind inflation is that almost immediately after the Big Bang, our entire universe entered into a not entirely stable energy state known as a false vacuum. The term is a bit misleading, because what scientists mean by “vacuum” in this case is actually “ground state”; “false vacuum” is just another way of saying that the universe is in an elevated energy state. The negative pressure of this state causes all of space to expand exponentially quickly.

Obviously, our universe isn’t still in this growth spurt — otherwise we wouldn’t even be able to see neighboring galaxies. The expansion of space would have long since have spirited them out of sight. Somehow, at least our local universe had to come out of this phase.

Shortly after Alan Guth formulated the idea of inflation, scientists including Paul Steinhardt (then at University of Pennsylvania) and Alexander Vilenkin (Tufts University), figured out that quantum fluctuations could do the trick for ending the inflationary era. A pocket of space could spontaneously come out of inflation, settling into a relatively sedate phase of expansion. But, quantum fluctuations being random, inflation would stop here and there rather than everywhere at once. Meanwhile, far beyond what we can observe, space keeps inflating at an exponential rate. Even as quantum fluctuations cause other pockets of space to similarly come out of inflation, the universe as a whole would keep growing exponentially — forever.

If inflation is really eternal, then our cosmos is one of an infinite variety of universes (known as the multiverse), each following an infinite variety of physical laws.

Stephen Hawking gives a presentation in 2003 to a backdrop of the all-sky cosmic microwave background map from the WMAP satellite.

At least, that’s the conclusion cosmologists reach when treating quantum effects as small relative to a universe largely dominated by relativity. “But I have never been a fan of the multiverse,” Hawking said in an interview last fall. “If the scale of different universes in the multiverse is large or infinite the theory can’t be tested.”

Instead, Hawking and Hertog argue, relativity would break down in the early universe; only quantum theory applies. Treating the universe as a single, tiny particle, they compute its wave function: a single equation that describes all the possible states our universe could take.

In order to do this, they first simplify the math in some seemingly strange ways. First, they assume a simple universe, one without matter or energy, with an overall geometry that’s saddle-shaped. Of course, we don’t actually live in a universe without matter or energy, and the universe’s geometry appears to be flat as a sheet of a paper rather than saddle-shaped, but this is the starting point that many cosmologists take to work out new theories.

But that’s not all. They also assume that they can treat this universe as a hologram. Yes, really — it sounds weird, but basically what they’re doing is reducing three-dimensional equations into two-dimensional equations projected onto a surface. (It doesn’t mean our universe is a hologram, just that we can mathematically treat it like one.)

Rather than reducing a spatial dimension, though, what Hawking and Hertog remove is time. Relativity is no longer necessary in a timeless universe, and the pair could rely instead solely on quantum theory.

From there, Hawking and Hertog solve the equations and come to an astounding conclusion: the universe that emerges from inflation is finite. We still live in a multiverse, but now it’s one with limited possibilities.

However, Vilenkin urges caution in interpreting these results, noting that the simplified mathematical treatment, and the conclusions Hawking and Hertog derive from it, might not apply to our real, more complicated universe. “I am sure Thomas Hertog will try to go beyond this model,” Vilenkin adds, “but it is hard to tell how successful this is going to be.”

 

Story Source:

By: Monica Young

 

Cosmos by John Hussey

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Early Star Formation Presents New Cosmic Mystery

Cosmos by John Hussey


New observations suggest that stars began forming just 250 million years after the Big Bang — a record-breaker that will likely open a new line of cosmological inquiry.

The galaxy cluster MACS J1149.5+2223 features in this image taken with the Hubble Space Telescope. The inset shows ALMA’s view of oxygen (green) in the galaxy MACS1149-JD1, whose light has traveled 13.28 billion light-years to Earth.

Inset: ALMA (ESO / NAOJ / NRAO) / Hashimoto et al.; Background: NASA / ESA Hubble Space Telescope / W. Zheng (JHU) / M. Postman (STScI) / CLASH Team

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Because only hydrogen, helium, and a little lithium emerged from the Big Bang, the young universe was pristine. It wasn’t until the first generation of stars exploded, breathing carbon, oxygen and other heavy elements into the cosmos, that the universe’s inventory of elements increased. So, the detection of oxygen 550 million years after the Big Bang suggests that a generation of stars had already formed and died by this point.

Hashimoto and his colleagues estimate that the first generation of stars would have formed 250 million years after the Big Bang — even though Planck measurements of the cosmic microwave background indicate that star formation wouldn’t have been prevalent in this epoch. That said, the results are in line with a tentative result from the EDGES experiment, which found a signal from stars forming just 180 million years after the Big Bang. The EDGES result still awaits confirmation from other groups performing similar experiments.

For decades, teams of scientists have been racing to find the signatures of the first stars — and it’s more than cosmic curiosity. “There is renewed optimism we are getting closer and closer to witnessing directly the birth of starlight,” says coauthor Richard Ellis (University College London) in a press release. “Since we are all made of processed stellar material, this is really finding our own origins.”

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An Explosive Start

What’s more, the team also used infrared data taken with the Hubble Space Telescope and the Spitzer Space Telescope to glean the number of stars within the galaxy. Typically, galaxies form a small number of high-mass stars and a large number of low-mass stars. The high-mass stars die first, exploding as supernovae a few million years after they form. But the lowest-mass stars can survive for trillions of years — much longer than the age of the universe.

But Hashimoto and his colleagues saw that the galaxy contained even fewer few high-mass stars than expected — meaning that the star formation kicked-off strong, tapered off, and then started forming stars again. That’s the opposite of predictions from simulations of the early universe. The star formation rate was expected to increase with time at these early epochs, starting out slow and then growing exponentially — at least for high-mass galaxies like the one Hashimoto’s team detected.

“It may mean that we don’t really understand the first generation of galaxies sufficiently well,” says coauthor Erik Zackrisson (Uppsala University, Sweden). “There might be some ingredient that is missing from the simulations.”

Discovering that missing ingredient will be the goal of future work, but Zackrisson has a few ideas. It could be that the very first generation of stars produced far more powerful supernovae than theorists suspect. Or perhaps this particular galaxy hosts a ravenous supermassive black hole. Both would unleash powerful winds that would push gas away from the galaxy and suppress further star formation.

Rychard Bouwens (Leiden University, The Netherlands), who was not involved in the study, argues that the paper’s conclusions are reliable yet uncertain only because the team is peering so far back into the universe’s history. “It’s always this way when you’re at the cutting edge,” he says. “It might be providing us with important clues to what happened at very early times in the universe, but we can’t be sure until we observe more objects.”

Both Bouwens and Zackrisson are excited for the 2020 launch of the James Webb Space Telescope, which will be able to directly image galaxies at these early times. Not only that, but Webb is expected to image hundreds if not thousands of these young galaxies. As such, Bouwens compares the current observations to standing on a ship that is enveloped in a thick fog. Although you might be able to see the hazy outline of a lighthouse with Hubble or Spitzer, the James Webb Space Telescope will act like rays of sunlight — forcing the fog to clear and allowing us to see the lighthouse clearly, as well as the rocky coast behind it.

 

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By: Shannon Hall

 

Cosmos by John Hussey

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Too Many Massive Stars in Universe’s Youngest Galaxies

Cosmos by John Hussey


A new method of measuring star formation in the earliest galaxies finds that they’re producing more massive stars than expected — a result that could affect our understanding of how galaxies grow their stars.

The Tarantula Nebula  in the Large Magellanic Cloud is one of the largest star-forming regions in the Local Group of galaxies. Measurements have shown that it might be forming more massive stars than expected.

NASA / ESA / D. Lennon / E. Sabbi (STSCI) et al.

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But it’s difficult to reach such conclusions on the basis of a single star-forming region, no matter how well it has been studied. Now, new work appearing in Nature appears to confirm that star formation depends not on fundamental processes but on environment. Astronomers may have to do some rethinking after all.

 

Four Distant Starbursts

The focus in this study turns to four galaxies whose light took more than 10 billion years to travel to Earth. These galaxies are bursting with stars, but they’re also dusty, which makes them immune to methods requiring ultraviolet, visible, or infrared light. Instead, Zhi-Yu Zhang (University of Edinburgh, UK, and European Southern Observatory, Germany) and colleagues trained the Atacama Millimeter/submillimeter Array (ALMA) on these galaxies, searching for emission related to carbon monoxide, a signal tied to a galaxy’s history of star formation.

ALMA’s incredible resolving power received a helping hand in the form of gravitational lenses: foreground galaxies aligned just so. Their gravity acted as a cosmic lens to magnify the light from these distant starbursts.

 

ALMA images distant starburst galaxies

ALMA imaged emission from 13CO (top) and C18O (bottom) molecules in four distant starburst galaxies. The ratio of these two isotopologues allowed astronomers to determine that these starburst galaxies have an excess of massive stars.

The scientists measured two isotopologs of carbon monoxide: 13CO and C18O. 13C, (which contains one more neutron than ordinary carbon atoms) is released by stars of all masses, whereas 18O (which contains two extra neutrons compared to ordinary oxygen atoms) is released by only by more massive stars. Since more massive stars live brief lives, measuring the abundance of 13CO and C18O serves as a fossil record of how many massive stars formed relative to low-mass stars.

The signature is immune to what the study authors describe as “pernicious” effects of dust. But the authors also acknowledge that the measurement is a roundabout way of getting at the problem.

That’s because they’re observing carbon monoxide molecules that are floating in the gas between the stars, rather than measuring radiation from stars themselves. So they’re in effect probing the galaxy’s entire history of star formation. Granted, galaxies in the early universe have a shorter history and thus a shorter amount of time for confounding effects to complicate the measurements, but as Kevin Covey (Western Washington University) points out, it’s still possible.

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Dusty starburst galaxy (art)

This artist’s impression shows a dusty galaxy in the distant universe. New ALMA observations have allowed scientists to lift the veil of dust and see what was previously inaccessible — that such starburst galaxies have an excess of massive stars as compared to more peaceful galaxies.

 

Redefining Cosmic Noon

If the measurements hold up, then what we dub “starburst” galaxies in the early universe aren’t actually making as many stars as we thought. Most stars have less than the Sun’s mass, but these young galaxies appear to be pouring more of their energy into making more massive stars. That means that other methods of estimating star formation rates might be wrong. In fact, our entire understanding of the cosmic star formation — which astronomers currently think peaked when the universe was roughly 4 billion years old — might be wrong.

Profound implications aside, Zhang’s team has a ways to go when it comes to convincing all of their colleagues. But they’re only getting started: Zhang says they’re already preparing more systematic surveys that will include nearby galaxies and multiple tracers of star formation.

 

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By: Monica Young

 

Cosmos by John Hussey

 

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Pulsar Limits “Fifth Force” Interactions with Dark Matter

Cosmos by John Hussey


A recent experiment to better understand the nature of dark matter constrains a possible “fifth force” of nature to almost zero.

An artist’s illustration shows what pulsar PSR J1713+0747 and its white dwarf companion might look like.

ESO / L. Calçada

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Scientists recently studied a pulsar binary system to constrain the existence of a hypothetical fifth fundamental force of nature.

We already know about four fundamental forces: gravity, electromagnetism, and the strong and weak nuclear forces. However, there are some effects in the universe that cannot be explained by these forces alone. For example, a 2016 experiment in Hungary showed unexpected behavior in the decay of nuclei in the isotype beryllium-8. (After shooting protons at lithium foil, observers saw more electron-positron pairs ejected at a 140-degree angle, which is difficult to explain with standard nuclear physics theories.)

One possibility is the existence of a “fifth force” of nature, which governs the behavior of elementary particles alongside the other four forces. Some scientists suggest this force could work on dark matter, the unseen substance that makes up most of the universe’s mass. We can see dark matter’s effects on ordinary matter, but direct detection has eluded scientists and what it’s made of remains unknown.

 

Testing for a Fifth Force

One research group tested for a fifth force using a pulsar and its white dwarf star companion. Pulsars, whose atoms have been compacted into neutrons, are so dense that their extreme gravitational fields could enhance any possible interactions with dark matter. The white dwarf, while still sardine-packing its atoms, isn’t nearly so compact. General relativity predicts that normal matter ought to fall freely toward dark matter, but a fifth force that has the ability to interact with both normal and dark matter could strengthen or diminish dark matter’s pull. If a fifth force does exist, the Milky Way’s dark matter halo, whose density ought to peak in the galactic center, would pull on the neutron star and the white dwarf in different ways, slightly altering their orbit.

The researchers chose binary pulsar PSR J1713+0747, which is 3,800 light-years from Earth, lying in the direction of the galactic center. Dark matter is believed to be more populous towards the heart of the galaxy, so the pulsar binary system provides an ideal test how a fifth force would act on dark matter and standard matter. The researchers wanted to see if the movements of the pulsar and white dwarf would differ as they orbited one another.

“If there is a fifth force that acts between dark matter and standard matter, it would not be universal,” says Lijing Shao (Max Planck Institute for Radio Astronomy, Germany). “It would therefore produce an apparent difference for the neutron star and the white dwarf in their free fall towards dark matter. Thus, the orbit of the neutron star would be different than what is predicted by the general relativity.”

Using 20 years of radio observations of this system, the researchers concluded that if a fifth force does exist, it must have less than 1% of gravity’s strength . (And gravity is already the weakest of the four known forces.) The results appear in Physical Review Letters.

The researchers also discovered that the limits on the density of dark matter at this pulsar system were similar to other tests closer to Earth. In other words, the team didn’t prove or disprove other observations showing that dark matter density increases towards the center of the galaxy.

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Beyond Relativity

Aurélien Hees (Observatory of Paris), who was not involved in the study, noted that this work is the first to investigate interactions between a hypothetical fifth force and dark matter in this way. The short rotational period of the pulsar – just 4.6 milliseconds – and its stable rotation made it a good candidate for constraining the effects of the fifth force, he said.

With the fifth force, he explains, “We expect to see something a little bit beyond relativity. We are trying to search for that with all the observations available from Earth.”

Shao says his team hopes to study more binary pulsars closer to the center of the galaxy to better understand the effects of dark matter. Unlike most tests of general relativity, in this case the researchers want to find pulsars moving in relatively slow orbits around their companion The challenge, of course, is finding the pulsars in the first place. He suggested a breakthrough will come when the more sensitive Square Kilometer Array is ready in the 2020s. “Bigger radio telescopes and arrays are better because they more precisely measure the time of the [pulsar signal] arrival,” Shao said.

 

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By: Elizabeth Howell

 

Cosmos by John Hussey

 

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Best Test of General Relativity on Galaxy Scales

Cosmos by John Hussey


Astronomers have conducted the best, galaxy-scale test of general relativity yet, and it rules out some (but not all) theories of modified gravity.

An image of the nearby galaxy ESO 325-G004, created using data collected by the NASA/ESA Hubble Space Telescope and the MUSE instrument on the ESO’s Very Large Telescope. The inset shows the Einstein ring resulting from the distortion of light from a more distant source by intervening lens ESO 325-004, which becomes visible after subtraction of the foreground lens light.

ESO / ESA / Hubble / NASA

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Collett and colleagues first calculated the mass of the intervening galaxy by measuring the movements of stars within it. Then they measured the spatial curvature generated by each unit mass of the intervening galaxy. The mass inferred by spacetime curvature is precisely consistent with the mass measured by the stars, exactly as general relativity predicts.

Unlike previous lensing tests of relativity, Collett’s team relied less on assumptions about the nature of the intervening galaxy. So this test is relatively free of systematic uncertainties that have plagued previous studies.

Lucas Lombriser (University of Geneva), who was not involved in the study, calls the measurements, “the most robust test of gravity of this type and on these length scales to date.”

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“However,” he adds, “while this new test rules out some alternative gravity theories, there are many others that remain compatible with the measurement.” While this study limited any variations in gravity on scales less than 6,500 light-years, additional tests will still be needed to rule out modified gravity more generally.

 

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By: Monica Young

 

Cosmos by John Hussey

 

Best Test of General Relativity on Galaxy Scales

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HaloSat: A Small Satellite for a Big Question

Cosmos by John Hussey


HaloSat, a mini-satellite recently deployed from the International Space Station, is on the hunt for the universe’s missing matter.

An artist’s conception of HaloSat in space.

Blue Canyon Technologies

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A small CubeSat mission may provide the data that answers a key cosmological question: where is half of the ordinary matter in the universe?

When astronomers attempt to measure the universe’s total baryonic mass using modern surveys, they keep coming up short. The team behind HaloSat, built by Blue Canyon Technologies and run by the University of Iowa, looks to answer this question by looking at X-ray emissions from the gaseous halo thought to surround the Milky Way Galaxy.

The current tally of the universe’s mass and energy distribution comes from analysis of the Cosmic Microwave Background (CMB), radiation released when the infant universe was just 370,000 years old. Measurements of this early era show that the universe is a mix of 70% dark energy, 25% dark matter, and 5% baryonic matter — the “normal” stuff, including protons, neutrons, and electrons, that makes up the stars, planets, spacecraft, and humans.

Yet astronomers tallying up the observable measure of stars, planets, galaxies, gas, and dust only come up with about half of the baryonic mass they expect.

“We should have all the matter today that we had back when the Universe was 400,000 years old,” Philip Kaaret (University of Iowa) said in a recent press release. Finding the missing matter “can help us learn how we got from the CMB’s uniform state to the large-scale structures we see today.”

One proposed location for the missing mass is the hot gas in the space between galaxies or in the halos around galaxies. For example, gas in the Milky Way’s halo should run around 2 million Kelvin. HaloSat was designed, among other things, to detect the X-rays emitted by ionized oxygen associated with this gas.

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View Sample Video – Cosmology – Telescopes – Hubble – 15 Years of Discovery

Probing the Galactic Halo

There’s one key problem to detecting this emission: The solar wind interacts with Earth’s atmosphere to produce X-rays that swamp any signal from the galactic halo.

“Every observation we make has this solar wind emission in it to some degree, but it varies with the time and solar wind conditions,” Kip Kuntz (Johns Hopkins University) said in a recent press release. “The variations are so hard to calculate that many people just mention it and then ignore it in their observations.”

HaloSat will get around this by making observations during the 45-minute passes over Earth’s nightside, recharging its solar-powered batteries during the daytime half of its 90-minute orbit.

HaloSat detects X-rays with energies between 400 and 2,000 electron-volts, the same regime as the Chandra and XMM-Newton space telescopes. But unlike these other orbiting X-ray observatories, HaloSat has a wide field of view, 100 square degrees, allowing it to carry out an efficient survey of the entire sky.

Researchers hope to use HaloSat to discern the shape of the Milky Way’s galactic gas halo, to see if it follows more of the bulging pancake shape (the fried egg model) of the Milky Way galaxy itself, or is more of a sphere. If the distribution isn’t uniform, HaloSat should see the difference, looking out perpendicular to the plane of the galaxy versus along the plane itself.

 

Launch & Deployment

HaloSat was launched from NASA’s Wallops Flight Facility on the Virginia coast on May 21, 2018, aboard the Cygnus S.S. J.R. Thompson spacecraft en route to the International Space Station. It was released from the ISS on July 13th.

Halosat is built around an XB1 CubeSat bus from Blue Canyon Technologies, and is equipped with reaction wheels, star trackers, and a solar panel. Although it’s equipped for a wide-field survey, it has a pointing accuracy of better than 30 arc seconds. Its three X-ray detectors were built by Amptek Inc, and are similar to the ones on NASA’s Neutron star Interior Composition Explorer aboard the ISS.

“We expect to operate HaloSat for one year,” says Kaaret. “We hope to show some preliminary results on one or a few bright targets within the Milky Way within that year, mostly to show how the instrument is operating. The results on the halo and the missing baryon problem will hopefully come 6-12 months after operations are done.”

It will be amazing to see if a small satellite mission such as HaloSat can answer such a big cosmological mystery.

Story Source:

By: David Dickinson

 

Cosmos by John Hussey

 

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New insight into why galaxies stop forming stars

Cosmos by John Hussey


Galaxy clusters are rare regions of the universe consisting of hundreds of galaxies containing trillions of stars. It has long been known that when a galaxy falls into a cluster, star formation is fairly rapidly shut off in a process known as ‘quenching.’ A new study has made the best measurement yet of the quenching timescale, measuring how it varies across 70 percent of the history of the universe.

Hubble Space Telescope image of one of the SpARCS clusters used in the study, seen as it appeared when the universe was 4.8 billion years old.

Credit: Jeffrey Chan, UC Riverside.

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Galaxy clusters are rare regions of the universe consisting of hundreds of galaxies containing trillions of stars, as well as hot gas and dark matter.

It has long been known that when a galaxy falls into a cluster, star formation is fairly rapidly shut off in a process known as “quenching.” What actually causes the stars to quench, however, is a mystery, despite several plausible explanations having been proposed by astronomers.

A new international study led by astronomer Ryan Foltz, a former graduate student at the University of California, Riverside, has made the best measurement yet of the quenching timescale, measuring how it varies across 70 percent of the history of the universe. The study has also revealed the process likely responsible for shutting down star formation in clusters.

Each galaxy entering a cluster is known to bring some cold gas with it that has not yet formed stars. One possible explanation suggests that before the cold gas can turn into stars, it is “stripped” away from the galaxy by the hot, dense gas already in the cluster, causing star formation to cease.

Another possibility is that galaxies are instead “strangled,” meaning they stop forming stars because their reservoirs cease getting replenished with additional cold gas once they fall inside the cluster. This is predicted to be a slower process than stripping.

A third possibility is that energy from the star formation itself drives much of the cold gas fuel away from the galaxy and prevents it from forming new stars. This “outflow” scenario is predicted to occur on a faster timescale than stripping, because the gas is lost forever to the galaxy and is unavailable to form new stars.

Because these three different physical processes predict galaxies to quench on different relative timescales over the history of the universe, astronomers have postulated that if they could compare the number of quenched galaxies observed over a long time-baseline, the dominant process causing stars to quench would more readily become apparent.

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However, until recently, it was very difficult to find distant clusters, and even harder to measure the properties of their galaxies. The international Spitzer Adaptation of the Red-sequence Cluster Survey, or SpARCS, survey has now made a measurement of more than 70 percent of the history of the universe, accomplished by pioneering new cluster-detection techniques, which enabled the discovery of hundreds of new clusters in the distant universe.

Using some of their own newly discovered SpARCS clusters, the new UCR-led study discovered that it takes a galaxy longer to stop forming stars as the universe gets older: only 1.1 billion years when the universe was young (4 billion years old), 1.3 billion years when the universe is middle-aged (6 billion years old), and 5 billion years in the present-day universe.

“Comparing observations of the quenching timescale in galaxies in clusters in the distant universe to those in the nearby universe revealed that a dynamical process such as gas stripping is a better fit to the predictions than strangulation or outflows,” Foltz said.

To make this state-of-the art measurement, the SpARCS team required 10 nights of observations with the W. M. Keck Observatory telescopes (10 meters in diameter) in Hawaii, and 25 nights of observations with the twin Gemini telescopes (8 meters in diameter) in Hawaii and Chile.

“Thanks to the phenomenal investment in our work by these observatories, we now believe we have a good idea of how star formation stops in the most massive galaxies in clusters,” said Gillian Wilson, professor of physics and astronomy at UCR and leader of the SpARCS survey, in whose lab Foltz worked when the study was done. “There are good reasons, however, to believe that lower-mass galaxies may quench by a different process. That is one of the questions our team is working on answering next.”

The team has been awarded 50 additional nights of Gemini time and a $1.2 million grant from the National Science Foundation to study how star formation stops in more regular-mass galaxies. Wilson was also awarded Hubble Space Telescope observations and a NASA grant to analyze high-resolution images of the quenching galaxies.

The research paper is published in the Astrophysical Journal.

 

Story Source:

Materials provided by University of California – Riverside.

 

Cosmos by John Hussey

 

https://www.sciencedaily.com/releases/2018/10/181023185443.htm

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Superflares from young red dwarf stars imperil planets

Cosmos by John Hussey


Flares from the youngest red dwarfs surveyed are 100 to 1,000 times more energetic than when the stars are older. This younger age is when terrestrial planets are forming around their stars.

Violent outbursts of seething gas from young red dwarf stars may make conditions uninhabitable on fledgling planets. In this artist’s rendering, an active, young red dwarf (right) is stripping the atmosphere from an orbiting planet (left). Scientists found that flares from the youngest red dwarfs they surveyed — approximately 40 million years old — are 100 to 1,000 times more energetic than when the stars are older. They also detected one of the most intense stellar flares ever observed in ultraviolet light — more energetic than the most powerful flare ever recorded from our Sun.

Credit: NASA, ESA and D. Player (STScI)

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The word “HAZMAT” describes substances that pose a risk to the environment, or even to life itself. Imagine the term being applied to entire planets, where violent flares from the host star may make worlds uninhabitable by affecting their atmospheres.

NASA’s Hubble Space Telescope is observing such stars through a large program called HAZMAT — Habitable Zones and M dwarf Activity across Time.

“M dwarf” is the astronomical term for a red dwarf star — the smallest, most abundant and longest-lived type of star in our galaxy. The HAZMAT program is an ultraviolet survey of red dwarfs at three different ages: young, intermediate, and old.

Stellar flares from red dwarfs are particularly bright in ultraviolet wavelengths, compared with Sun-like stars. Hubble’s ultraviolet sensitivity makes the telescope very valuable for observing these flares. The flares are believed to be powered by intense magnetic fields that get tangled by the roiling motions of the stellar atmosphere. When the tangling gets too intense, the fields break and reconnect, unleashing tremendous amounts of energy.

The team has found that the flares from the youngest red dwarfs they surveyed — just about 40 million years old — are 100 to 1,000 times more energetic than when the stars are older. This younger age is when terrestrial planets are forming around their stars.

Approximately three-quarters of the stars in our galaxy are red dwarfs. Most of the galaxy’s “habitable-zone” planets — planets orbiting their stars at a distance where temperatures are moderate enough for liquid water to exist on their surface — likely orbit red dwarfs. In fact, the nearest star to our Sun, a red dwarf named Proxima Centauri, has an Earth-size planet in its habitable zone.

However, young red dwarfs are active stars, producing ultraviolet flares that blast out so much energy that they could influence atmospheric chemistry and possibly strip off the atmospheres of these fledgling planets.

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“The goal of the HAZMAT program is to help understand the habitability of planets around low-mass stars,” explained Arizona State University’s Evgenya Shkolnik, the program’s principal investigator. “These low-mass stars are critically important in understanding planetary atmospheres.”

The results of the first part of this Hubble program are being published in The Astrophysical Journal. This study examines the flare frequency of 12 young red dwarfs. “Getting these data on the young stars has been especially important, because the difference in their flare activity is quite large as compared to older stars,” said Arizona State University’s Parke Loyd, the first author on this paper.

The observing program detected one of the most intense stellar flares ever observed in ultraviolet light. Dubbed the “Hazflare,” this event was more energetic than the most powerful flare from our Sun ever recorded.

“With the Sun, we have a hundred years of good observations,” Loyd said. “And in that time, we’ve seen one, maybe two, flares that have an energy approaching that of the Hazflare. In a little less than a day’s worth of Hubble observations of these young stars, we caught the Hazflare, which means that we’re looking at superflares happening every day or even a few times a day.”

Could super-flares of such frequency and intensity bathe young planets in so much ultraviolet radiation that they forever doom chances of habitability? According to Loyd, “Flares like we observed have the capacity to strip away the atmosphere from a planet. But that doesn’t necessarily mean doom and gloom for life on the planet. It just might be different life than we imagine. Or there might be other processes that could replenish the atmosphere of the planet. It’s certainly a harsh environment, but I would hesitate to say that it is a sterile environment.”

The next part of the HAZMAT study will be to study intermediate-aged red dwarfs that are 650 million years old. Then the oldest red dwarfs will be analyzed and compared with the young and intermediate stars to understand the evolution of the ultraviolet radiation environment of low-mass planets around these low-mass stars.

 

Story Source:

Materials provided by NASA/Goddard Space Flight Center.

 

Cosmos by John Hussey

 

https://www.sciencedaily.com/releases/2018/10/181018141204.htm

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Andromeda galaxy scanned with high-energy X-ray vision

Cosmos by John Hussey


NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured the best high-energy X-ray view yet of a portion of our nearest large, neighboring galaxy, Andromeda. The space mission has observed 40 “X-ray binaries” — intense sources of X-rays composed of a black hole or neutron star that feeds off a stellar companion.

NASA’s Nuclear Spectroscope Telescope Array, or NuSTAR, has imaged a swath of the Andromeda galaxy — the nearest large galaxy to our own Milky Way galaxy.

Credit: NASA/JPL-Caltech/GSFC

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NASA’s Nuclear Spectroscopic Telescope Array, or NuSTAR, has captured the best high-energy X-ray view yet of a portion of our nearest large, neighboring galaxy, Andromeda. The space mission has observed 40 “X-ray binaries” — intense sources of X-rays composed of a black hole or neutron star that feeds off a stellar companion.

The results will ultimately help researchers better understand the role of X-ray binaries in the evolution of our universe. According to astronomers, these energetic objects may play a critical role in heating the intergalactic bath of gas in which the very first galaxies formed.

“Andromeda is the only large spiral galaxy where we can see individual X-ray binaries and study them in detail in an environment like our own,” said Daniel Wik of NASA Goddard Space Flight Center in Greenbelt, Maryland, who presented the results at the 227th meeting of American Astronomical Society in Kissimmee, Florida.¬¬¬¬ “We can then use this information to deduce what’s going on in more distant galaxies, which are harder to see.”

Andromeda, also known as M31, can be thought of as the big sister to our own Milky Way galaxy. Both galaxies are spiral in shape, but Andromeda is slightly larger than the Milky Way in size. Lying 2.5 million light-years away, Andromeda is relatively nearby in cosmic terms. It can even be seen by the naked eye in dark, clear skies.

Other space missions, such as NASA’s Chandra X-ray Observatory, have obtained crisper images of Andromeda at lower X-ray energies than the high-energy X-rays detected by NuSTAR. The combination of Chandra and NuSTAR provides astronomers with a powerful tool for narrowing in on the nature of the X-ray binaries in spiral galaxies.

In X-ray binaries, one member is always a dead star or remnant formed from the explosion of what was once a star much more massive than the sun. Depending on the mass and other properties of the original giant star, the explosion may produce either a black hole or neutron star. Under the right circumstances, material from the companion star can “spill over” its outermost edges and then be caught by the gravity of the black hole or neutron star. As the material falls in, it is heated to blazingly high temperatures, releasing a huge amount of X-rays.

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With NuSTAR’s new view of a swath of Andromeda, Wik and colleagues are working on identifying the fraction of X-ray binaries harboring black holes versus neutron stars. That research will help them understand the population as a whole.

“We have come to realize in the past few years that it is likely the lower-mass remnants of normal stellar evolution, the black holes and neutron stars, may play a crucial role in heating of the intergalactic gas at very early times in the universe, around the cosmic dawn,” said Ann Hornschemeier of NASA Goddard, the principal investigator of the NuSTAR Andromeda studies.

“Observations of local populations of stellar-mass-sized black holes and neutron stars with NuSTAR allow us to figure out just how much power is coming out from these systems.”

The new research also reveals how Andromeda may differ from our Milky Way. Fiona Harrison, the principal investigator of the NuSTAR mission, added, “Studying the extreme stellar populations in Andromeda tells us about how its history of forming stars may be different than in our neighborhood.”

Harrison will be presenting the 2015 Rossi Prize lecture at the AAS meeting. The prize, awarded by the AAS’s High-Energy Astrophysics Division, honors physicist Bruno Rossi, an authority on cosmic-ray physics and a pioneer in the field of X-ray astronomy.

 

For more information about NuSTAR, visit:

http://www.nustar.caltech.edu/

 

Story Source:

Materials provided by NASA/Jet Propulsion Laboratory.

 

Cosmos by John Hussey

 

https://www.sciencedaily.com/releases/2016/01/160105160351.htm

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Globular clusters could host interstellar civilizations

Cosmos by John Hussey


Globular star clusters are extraordinary in almost every way. They’re densely packed, holding a million stars in a ball only about 100 light-years across on average. They’re old, dating back almost to the birth of the Milky Way. And according to new research, they also could be extraordinarily good places to look for space-faring civilizations.

Globular star clusters like this one, 47 Tucanae, might be excellent places to search for interstellar civilizations. Their crowded nature means intelligent life at our stage of technological advancement could send probes to the nearest stars.

Credit: NASA, ESA, and the Hubble Heritage Team

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Globular star clusters are extraordinary in almost every way. They’re densely packed, holding a million stars in a ball only about 100 light-years across on average. They’re old, dating back almost to the birth of the Milky Way. And according to new research, they also could be extraordinarily good places to look for space-faring civilizations.

“A globular cluster might be the first place in which intelligent life is identified in our galaxy,” says lead author Rosanne DiStefano of the Harvard-Smithsonian Center for Astrophysics (CfA).

DiStefano presented this research today in a press conference at a meeting of the American Astronomical Society.

Our Milky Way galaxy hosts about 150 globular clusters, most of them orbiting in the galactic outskirts. They formed about 10 billion years ago on average. As a result, their stars contain fewer of the heavy elements needed to construct planets, since those elements (like iron and silicon) must be created in earlier generations of stars. Some scientists have argued that this makes globular cluster stars less likely to host planets. In fact, only one planet has been found in a globular cluster to date.

However, DiStefano and her colleague Alak Ray (Tata Institute of Fundamental Research, Mumbai) argue that this view is too pessimistic. Exoplanets have been found around stars only one-tenth as metal-rich as our Sun. And while Jupiter-sized planets are found preferentially around stars containing higher levels of heavy elements, research finds that smaller, Earth-sized planets show no such preference.

“It’s premature to say there are no planets in globular clusters,” states Ray.

Another concern is that a globular cluster’s crowded environment would threaten any planets that do form. A neighboring star could wander too close and gravitationally disrupt a planetary system, flinging worlds into icy interstellar space.

However, a star’s habitable zone — the distance at which a planet would be warm enough for liquid water — varies depending on the star. While brighter stars have more distant habitable zones, planets orbiting dimmer stars would have to huddle much closer. Brighter stars also live shorter lives, and since globular clusters are old, those stars have died out. The predominant stars in globular clusters are faint, long-lived red dwarfs. Any potentially habitable planets they host would orbit nearby and be relatively safe from stellar interactions.

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“Once planets form, they can survive for long periods of time, even longer than the current age of the universe,” explains DiStefano.

So if habitable planets can form in globular clusters and survive for billions of years, what are the consequences for life should it evolve? Life would have ample time to become increasingly complex, and even potentially develop intelligence.

Such a civilization would enjoy a very different environment than our own. The nearest star to our solar system is four light-years, or 24 trillion miles, away. In contrast, the nearest star within a globular cluster could be about 20 times closer — just one trillion miles away. This would make interstellar communication and exploration significantly easier.

“We call it the ‘globular cluster opportunity,'” says DiStefano. “Sending a broadcast between the stars wouldn’t take any longer than a letter from the U.S. to Europe in the 18th century.”

“Interstellar travel would take less time too. The Voyager probes are 10 billion miles from Earth, or one-tenth as far as it would take to reach the closest star if we lived in a globular cluster. That means sending an interstellar probe is something a civilization at our technological level could do in a globular cluster,” she adds.

The closest globular cluster to Earth is still several thousand light-years away, making it difficult to find planets, particularly in a cluster’s crowded core. But it could be possible to detect transiting planets on the outskirts of globular clusters. Astronomers might even spot free-floating planets through gravitational lensing, in which the planet’s gravity magnifies light from a background star.

A more intriguing idea might be to target globular clusters with SETI search methods, looking for radio or laser broadcasts. The concept has a long history: In 1974 astronomer Frank Drake used the Arecibo radio telescope to broadcast the first deliberate message from Earth to outer space. It was directed at the globular cluster Messier 13 (M13).

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for Astrophysics (CfA) is a joint collaboration between the Smithsonian Astrophysical Observatory and the Harvard College Observatory. CfA scientists, organized into six research divisions, study the origin, evolution and ultimate fate of the universe.

 

Story Source:

Materials provided by Harvard-Smithsonian Center for Astrophysics.

 

Cosmos by John Hussey

 

https://www.sciencedaily.com/releases/2016/01/160106110659.htm

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