Galaxies that formed within the first few billion years after the Big Bang should have lived long, healthy lives. After all, they were born with rich supplies of cold hydrogen gas, exactly the fuel needed to continue star formation. But new observations have revealed “quenched” galaxies that have shut off star formation. And astronomers have no idea why.Continue reading “Early Massive Galaxies ran out of gas, Shutting Down Their Star Formation”
What happens when galaxies collide? Well, if any humans are around in about a billion years, they might find out. That’s when our Milky Way galaxy is scheduled to collide with our neighbour the Andromeda galaxy. That event will be an epic, titanic, collision. The supermassive black holes at the center of both galaxies will feast on new material and flare brightly as the collision brings more gas and dust within reach of their overwhelming gravitational pull. Where massive giant stars collide with each other, lighting up the skies and spraying deadly radiation everywhere. Right?
Maybe not. In fact, there might be no feasting at all, and hardly anything titanic about it.Continue reading “When Galaxies Collide, Black Holes Don’t Always Get the Feast They Were Hoping for”
Galaxies are supposed to build up a very slowly, taking billions of years to acquire their vast bulk. But a newfound galaxy, appearing in the universe when it was only 1.8 billion years old, tells a different tale. It formed stars at a rate hundreds of times greater than the Milky Way, and was able to build itself up to host 200 billion stars in less than 500 million years – perhaps the universe’s greatest speed run.Continue reading “This galaxy took only 500 million years to form”
Some galaxies are too small, and some galaxies are too big, while others are just right. A new survey of the nearby Virgo cluster has potentially revealed why extreme galaxies are the wrong size, and how they might be connected.Continue reading “Extreme galaxies depend on extreme conditions for their formation”
This galaxy looks a lot like our own Milky Way galaxy. But while our galaxy is actively forming lots of new stars, this one is birthing stars at only half the rate of the Milky Way. It’s been mostly quiet for billions of years, feeding lightly on the thin gas in intergalactic space.Continue reading “Hubble Captured a Photo of This Huge Spiral Galaxy, 2.5 Times Bigger than the Milky Way With 10 Times the Stars”
The first results of the IllustrisTNG Project have been published in three separate studies, and they’re shedding new light on how black holes shape the cosmos, and how galaxies form and grow. The IllustrisTNG Project bills itself as “The next generation of cosmological hydrodynamical simulations.” The Project is an ongoing series of massive hydrodynamic simulations of our Universe. Its goal is to understand the physical processes that drive the formation of galaxies.
At the heart of IllustriousTNG is a state of the art numerical model of the Universe, running on one of the most powerful supercomputers in the world: the Hazel Hen machine at the High-Performance Computing Center in Stuttgart, Germany. Hazel Hen is Germany’s fastest computer, and the 19th fastest in the world.
Our current cosmological model suggests that the mass-energy density of the Universe is dominated by dark matter and dark energy. Since we can’t observe either of those things, the only way to test this model is to be able to make precise predictions about the structure of the things we can see, such as stars, diffuse gas, and accreting black holes. These visible things are organized into a cosmic web of sheets, filaments, and voids. Inside these are galaxies, which are the basic units of cosmic structure. To test our ideas about galactic structure, we have to make detailed and realistic simulated galaxies, then compare them to what’s real.
Astrophysicists in the USA and Germany used IllustrisTNG to create their own universe, which could then be studied in detail. IllustrisTNG correlates very strongly with observations of the real Universe, but allows scientists to look at things that are obscured in our own Universe. This has led to some very interesting results so far, and is helping to answer some big questions in cosmology and astrophysics.
How Do Black Holes Affect Galaxies?
Ever since we’ve learned that galaxies host supermassive black holes (SMBHs) at their centers, it’s been widely believed that they have a profound influence on the evolution of galaxies, and possibly on their formation. That’s led to the obvious question: How do these SMBHs influence the galaxies that host them? Illustrious TNG set out to answer this, and the paper by Dr. Dylan Nelson at the Max Planck Institute for Astrophysics shows that “the primary driver of galaxy color transition is supermassive blackhole feedback in its low-accretion state.”
“The only physical entity capable of extinguishing the star formation in our large elliptical galaxies are the supermassive black holes at their centers.” – Dr. Dylan Nelson, Max Planck Institute for Astrophysics,
Galaxies that are still in their star-forming phase shine brightly in the blue light of their young stars. Then something changes and the star formation ends. After that, the galaxy is dominated by older, red stars, and the galaxy joins a graveyard full of “red and dead” galaxies. As Nelson explains, “The only physical entity capable of extinguishing the star formation in our large elliptical galaxies are the supermassive black holes at their centers.” But how do they do that?
Nelson and his colleagues attribute it to supermassive black hole feedback in its low-accretion state. What that means is that as a black hole feeds, it creates a wind, or shock wave, that blows star-forming gas and dust out of the galaxy. This limits the future formation of stars. The existing stars age and turn red, and few new blue stars form.
How Do Galaxies Form and How Does Their Structure Develop?
It’s long been thought that large galaxies form when smaller galaxies join up. As the galaxy grows larger, its gravity draws more smaller galaxies into it. During these collisions, galaxies are torn apart. Some stars will be scattered, and will take up residence in a halo around the new, larger galaxy. This should give the newly-created galaxy a faint background glow of stellar light. But this is a prediction, and these pale glows are very hard to observe.
“Our predictions can now be systematically checked by observers.” – Dr. Annalisa Pillepich (Max Planck Institute for Astrophysics)
IllustrisTNG was able to predict more accurately what this glow should look like. This gives astronomers a better idea of what to look for when they try to observe this pale stellar glow in the real Universe. “Our predictions can now be systematically checked by observers,” Dr. Annalisa Pillepich (MPIA) points out, who led a further IllustrisTNG study. “This yields a critical test for the theoretical model of hierarchical galaxy formation.”
IllustrisTNG is an on-going series of simulations. So far, there have been three IllustrisTNG runs, each one creating a larger simulation than the previous one. They are TNG 50, TNG 100, and TNG 300. TNG300 is much larger than TNG50 and allows a larger area to be studied which reveals clues about large-scale structure. Though TNG50 is much smaller, it has much more precise detail. It gives us a more detailed look at the structural properties of galaxies and the detailed structure of gas around galaxies. TNG100 is somewhere in the middle.
IllustrisTNG is not the first cosmological hydrodynamical simulation. Others include Eagle, Horizon-AGN, and IllustrisTNG’s predecessor, Illustris. They have shown how powerful these predictive theoretical models can be. As our computers grow more powerful and our understanding of physics and cosmology grow along with them, these types of simulations will yield greater and more detailed results.
On a clear night, you can make out the band of the Milky Way in the night sky. For millennia, astronomers looked upon it in awe, slowly coming to the realization that our Sun was merely one of billions of stars in the galaxy. Over time, as our instruments and methods improved, we came to realize that the Milky Way itself was merely one of billions of galaxies that make up the Universe.
Thanks to the discovery of Relativity and the speed of light, we have also come to understand that when we look through space, we are also looking back in time. By seeing an object 1 billion light-years away, we are also seeing how that object looked 1 billion years ago. This “time machine” effect has allowed astronomers to study how galaxies came to be (i.e. galactic evolution).
The process in which galaxies form and evolve is characterized by steady growth over time, which began shortly after the Big Bang. This process, and the eventual fate of galaxies, remain the subject of intense fascination, and is still fraught with its share of mysteries.
The current scientific consensus is that all matter in the Universe was created roughly 13.8 billion years ago during an event known as the Big Bang. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity. Suddenly, the Singularity began expanding, and the Universe as we know it began.
After rapidly expanding and cooling, all matter was almost uniform in distribution. Over the course of the several billion years that followed, the slightly denser regions of the Universe began to become gravitationally attracted to each other. They therefore grew even denser, forming gas clouds and large clumps of matter.
These clumps became primordial galaxies, as the clouds of hydrogen gas within the proto-galaxies underwent gravitational collapse to become the first stars. Some of these early objects were small, and became tiny dwarf galaxies, while others were much larger and became the familiar spiral shapes, like our own Milky Way.
Once formed, these galaxies evolved together in larger galactic structures called groups, clusters and superclusters. Over time, galaxies were attracted to one another by the force of their gravity, and collided together in a series of mergers. The outcome of these mergers depends on the mass of the galaxies in the collision.
Small galaxies are torn apart by larger galaxies and added to the mass of larger galaxies. Our own Milky Way recently devoured a few dwarf galaxies, turning them into streams of stars that orbit the galactic core. But when large galaxies of similar size come together, they become giant elliptical galaxies.
When this happens, the delicate spiral structure is lost, and the merged galaxies become large and elliptical. Elliptical galaxies are some of the largest galaxies ever observed. Another consequence of these mergers is that the supermassive black holes (SMBH) at their centers become even larger.
Not all mergers will result in elliptical galaxies, mind you. But all mergers result in a change in the structure of the merged galaxies. For example, it is believed that the Milky Way is experiencing a minor merger event with the nearby Magellanic Clouds; and in recent years, it has been determined that the Canis Major dwarf galaxy has merged with our own.
While mergers are seen as violent events, actual collisions are not expected to happen between star systems, given the vast distances between stars. However, mergers can result in gravitational shock waves, which are capable of triggering the formation of new stars. This is what is predicted to happen when our own Milky Way galaxy merges with the Andromeda galaxy in about 4 billion years time.
Ultimately, galaxies cease forming stars once they deplete their supply of cold gas and dust. As the supply runs out, star forming slows over the course of billions of years until it ceases entirely. However, ongoing mergers will ensure that fresh stars, gas and dust are deposited in older galaxies, thus prolonging their lives.
At present, it is believed that our galaxy has used up most of its hydrogen, and star formation will slow down until the supply is depleted. Stars like our Sun can only last for 10 billion years or so; but the smallest, coolest red dwarfs can last for a few trillion years. However, thanks to the presence of dwarf galaxies and our impending merger with Andromeda, our galaxy could exist even longer.
However, all galaxies in this vicinity of the Universe will eventually become gravitationally bound to each other and merge into a giant elliptical galaxy. Astronomers have seen examples of these sorts of “fossil galaxies”, a good of which is Messier 49 – a supermassive elliptical galaxy.
These galaxies have used up all their reserves of star forming gas, and all that’s left are the longer lasting stars. Eventually, over vast lengths of time, those stars will wink out one after the other, until the whole thing is the background temperature of the Universe.
After our galaxy merges with Andromeda, and goes on to merge with all other nearby galaxies in the local group, we can expect that it too will undergo a similar fate. And so, galaxy evolution has been occurring over billions of years, and it will continue to happen for the foreseeable future.
We have written many articles about galaxies for Universe Today. Here’s What is the Milky Way?, How did the Milky Way Form?, What Happens When Galaxies Collide?, What Happens When Galaxies Die?, A New Spin on Galactic Evolution, and Supercomputer will Study Galaxy Evolution,
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.
For decades astronomers have puzzled over the many details concerning the formation of the Milky Way Galaxy. Now a group of scientists headed by Ivan Minchev from the Leibniz Institute for Astrophysics Potsdam (AIP) have managed to retrace our galaxy’s formative periods with more detail than ever before. This newly published information has been gathered through careful observation of stars located near the Sun and points to a rather “moving” history.
To achieve these latest results, astronomers observed stars perpendicular to the galactic disc and their vertical motion. Just to shake things up, these stars also had their ages considered. Because it is nearly impossible to directly determine a star’s true age, they rattled the cage of chemical composition. Stars which show an increase in the ratio of magnesium to iron ([Mg/Fe]) appear to have a greater age. These determinations of stars close to the Sun were made with highly accurate information gathered by the RAdial Velocity Experiment (RAVE). According to previous findings, “the older a star is, the faster it moves up and down through the disc”. This no longer seemed to be true. Apparently the rules were broken by stars with the highest magnesium-to-iron ratios. Despite what astronomers thought would happen, they observed these particular stars slowing their roll… their vertical speed decreasing dramatically.
So what’s going on here? To help figure out these curious findings, the researchers turned to computer modeling. By running a simulation of the Milky Way’s evolutionary patterns, they were able to discern the origin of these older, slower stars. According to the simulation, they came to the conclusion that small galactic collisions might be responsible for the results they had directly observed.
Smashing into, or combining with, a smaller galaxy isn’t new to the Milky Way. It is widely accepted that our galaxy has been the receptor of galactic collisions many times during its course of history. Despite what might appear to be a very violent event, these incidents aren’t very good at shaking up the massive regions near the galactic center. However, they stir things up in the spiral arms! Here star formation is triggered and these stars move away from the core towards our galaxy’s outer edge – and near our Sun.
In a process known as “radial migration”, older stars, ones with high values of magnesium-to-iron ratio, are pushed outward and display low up-and-down velocities. Is this why the elderly, near-by stars have diminished vertical velocities? Were they forced from the galactic center by virtue of a collision event? Astronomers speculate this to be the best answer. By comparison, the differences in speed between stars born near the Sun and those forced away shows just how massive and how many merging galaxies once shook up the Milky Way.
Says AIP scientist Ivan Minchev: “Our results will enable us to trace the history of our home galaxy more accurately than ever before. By looking at the chemical composition of stars around us, and how fast they move, we can deduce the properties of satellite galaxies interacting with the Milky Way throughout its lifetime. This can lead to an improved understanding of how the Milky Way may have evolved into the galaxy we see today.”
Original Story Source: Leibniz Institute for Astrophysics Potsdam News Release. For further reading: A new stellar chemo-kinematic relation reveals the merger history of the Milky Way.
Nobody likes a sloppy COSMOS (Cosmological Evolution Survey) and astronomers utilizing the Fiber-Multi-Object Spectrograph (FMOS) mounted on the Subaru Telescope have put order into chaos through their studies. The survey has found that some nine billion years ago galaxies were capable of producing new stars in a fashion as orderly as game of checkers. Despite their young cosmological age, the galaxies show signs containing high amounts of dust enriched by heavier elements – a mature state.
“These findings center on a major question: What was the universe like when it was maximally forming its stars?” says John Silverman, the principal investigator of the FMOS-COSMOS project at the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU).
These “universal” questions are just what the COSMOS team seeks to answer. Their research goals are to enlighten the scales of cosmic time in relationship with the environment, formation and evolution of massive galactic structures. When studying individual galaxies, they may be able to tell if their rate of growth can be attributed to large-scale environments. Information of this type can clarify what factors the early Universe structure may have contributed to the current form of local galaxies. One of the data sets the team is focusing on is using the FMOS on the Subaru Telescope to chart out the distribution of more than a thousand galaxies which formed over nine billion years ago – a time when the Universe was hitting its star-formation peak.
“One key to generating fruitful results is collaboration between COSMOS researchers to maximize optimal use of FMOS.” Silverman continues, “In this project, researchers from Kavli IPMU in Japan and the Institute for Astronomy at the University of Hawaii (principal investigator: David Sanders) formed an effective collaboration to implement their goal.” The observations spanned 10 clear nights starting in March 2012.
Why choose spectroscopy? This advanced fiber optics technology speaks for itself, collecting light over an area of sky equal in size to that of the Moon. The FMOS focuses on the near-infrared, filtering out unwanted emissions caused by warm temperatures and can acquire spectra from 400 galaxies simultaneously with a wide field of coverage of 30 arc minutes at prime-focus. By employing such a wide field of view, astronomers can squeeze in a wide range of objects in their local environments. This enables researchers to maximize information on star-forming regions, cluster formation, and cosmology.
As David Sanders, the principal investigator of the FMOS-COSMOS project at IfA, puts it, “FMOS has clearly revolutionized our ability to study how galaxies form and evolve across cosmic time. It is currently the most powerful instrument we have to study the large numbers of objects needed to understand galaxies of all sizes, shapes and masses — from the largest ellipticals to the smallest dwarfs. We are extremely fortunate that the Kavli IPMU-IfA collaboration is giving us this unique opportunity to study the distant universe in such exquisite detail.”
FMOS will soon be famous by revealing its true potential. It has been collecting copious amounts of data in a high spectral resolution mode and at a very successful rate. So far it has accomplished nearly half of its goal – to examine over a thousand galaxies with redshifts to map the large-scale structure. The current survey consists of mapping an area of sky which spans a square degree in high-resolution mode and future plans for FMOS will involve enlarging the area. This expanded coverage will complement other instruments on alternative telescopes which have a wider spectral imaging system or a higher resolution which is limited to a smaller area. These combined findings may one day result in showing us some of the very first structures that eventually evolved into the massive galaxy clusters we see today!
Original Story Source: Kavli Institute for the Physics and Mathematics of the Universe News Release.
A giant spiral of gas dust and stars, Messier 101 spans 170,000 light-years and contains more than a trillion stars. Astronomers have uncovered a surprising trend in galaxy evolution where galaxies like M101 and the Milky Way Galaxy continued to develop into settled disk galaxies long after previously thought. Credit: NASA/ESA Hubble
Graceful in their turnings, spiral galaxies were thought to have reached their current state billions of years ago. A study of hundreds of galaxies, however, upsets that notion revealing that spiral galaxies, like the Andromeda Galaxy and our own Milky Way, have continued to change.
“Astronomers thought disk galaxies in the nearby universe had settled into their present form by about 8 billion years ago, with little additional development since,” said Susan Kassin, an astronomer at NASA’s Goddard Space Flight Center in Greenbelt, Md., and the study’s lead researcher in a press release. “The trend we’ve observed instead shows the opposite, that galaxies were steadily changing over this time period.”
A study of 544 star-forming galaxies observed by the Earth-based Keck and Hubble Space Telescope shows that disk galaxies like our Milky Way Galaxy unexpectedly reached their current state long after much of the universe’s star formation had ceased. Credit: NASA’s Goddard Space Flight Center
Astronomers used the twin 10-meter earth-bound W.M. Keck Observatory atop Hawaii’s Mauna Kea volcano and NASA’s Hubble Space Telescope to study 544 star-forming galaxies. Farther back in time, galaxies tend to be very different, say astronomers, with random and disorganized motions. Nearer to the present, star-forming galaxies look like well-ordered disk-shaped systems. Rotation in these galaxies trumps other internal, random motions. These galaxies are gradually settling into well-behaved disks with the most massive galaxies always showing higher organization.
This plot shows the fractions of settled disk galaxies in four time spans, each about 3 billion years long. There is a steady shift toward higher percentages of settled galaxies closer to the present time. At any given time, the most massive galaxies are the most settled. More distant and less massive galaxies on average exhibit more disorganized internal motions, with gas moving in multiple directions, and slower rotation speeds. Credit: NASA’s Goddard Space Flight Center
The sampling of galaxies studied, from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) Redshift Survey, ranged between 2 billion and 8 billion light-years from Earth with masses between 0.3 percent to 100 percent that of our own Milky Way Galaxy. Researchers looked at all galaxies in this time range with emission lines bright enough to determine internal motions. Researchers focused on emission lines characteristically emitted by gas within the galaxy. The emission lines not only tell scientists about the elements that make up the galaxies but also red shifting of emission lines contains information on the internal motions and distance.
“Previous studies removed galaxies that did not look like the well-ordered rotating disks now common in the universe today,” said co-author Benjamin Weiner, an astronomer at the University of Arizona in Tucson. “By neglecting them, these studies examined only those rare galaxies in the distant universe that are well-behaved and concluded that galaxies didn’t change.”
In the past 8 billion years, mergers between galaxies, both large and small, has decreased. So has the overall rate of star formation and associated disruptions due to supernovae explosions. Both factors may play a role in the newly found trend, say scientists.
The Milky Way Galaxy may have gone through the same chaotic growing and changing as the galaxies in the DEEP2 sample before settling into its present state at just about the same time the Sun and Earth were forming, say team scientists. By observing the pattern, astronomers can now adjust computer simulations of galaxy evolution until they replicate the observations. Then the hunt will be on to determine the physical processes responsible for the trend.
This cosmological simulation follows the development of a single disk galaxy throughout the life of the Universe; about 13.5 billion years. Red colors show old stars, young stars show as white and bright blue while the distribution of gas shows as a pale blue. The computer-generated view spans about 300,000 light-years. The simulation, running on the Pleiades supercomputer at NASA’s Ames Research Center in Moffett Field, California, took about 1 million CPU hours to complete. Credit: F. Governato and T. Quinn (Univ. of Washington), A. Brooks (Univ. of Wisconsin, Madison), and J. Wadsley (McMaster Univ.).
A paper detailing the findings will be published in the October 20, 2012 The Astrophysical Journal.