Jessica Walker, an astronomer at the University of Washington in Seattle, said at a meeting of the American Astronomical Society in June+10/October last year, "Galaxies are just like you and me. They live in a state of continuous chaos. "
Most turbulence occurs in a huge and complex environment, which is called CGM. This huge cloud of dust and natural gas is the fuel source, waste accumulation and recycling center of the Milky Way. Astronomers believe that the answers to the most pressing mysteries of galaxies are hidden in the surrounding medium (CGM), for example, how galaxies keep forming new stars for billions of years, and why the formation of stars suddenly stops.
Molly Pips, an astronomer at the Baltimore Space Telescope Science Institute, said: "To understand galaxies, you must understand the ecosystem in which they live."
However, the atmosphere of this galaxy is so dispersed that it is invisible, and the medium around a liter contains only one atom. Nearly 60 years later, the upgrade of Hubble Space Telescope began to detect distant surrounding media (CGM) and figured out how their constant agitation created or destroyed galaxies.
Until recently, we were able to truly observe the relationship between the gas circulation and the nature of the galaxy itself.
Through the first extragalactic survey, astronomers are now piecing together how the surrounding medium (CGM) controls the life and death of its galaxy. New theoretical research shows that if there is no crazy flow of medium, the stars in the galaxy will have very different arrangements. In addition, new observations show that some surrounding media (CGM) are surprisingly huge. Through new telescopes and computer simulations, we have a better understanding of the surrounding medium (CGM), which may change scientists' views on everything from the collision of galaxies to the origin of our own atoms.
Researchers use bright background light sources, such as quasars, to understand the environmental media around the galaxy, that is, the diffuse gas and metal clouds (pink in the picture) around the galaxy. Gas circulates between galaxies and CGM.
Waiting for Hubble telescope
The upgrade of Hubble telescope in 2009 made it possible to survey the surrounding medium (CGM), but this hardly happened.
Coincidentally, the main supporter of the Hubble telescope was also the first astronomer to discover how to observe the medium around the galaxy (CGM). Lyman Spitzer of Princeton University, johann bach of the Institute for Advanced Studies in Princeton, New Jersey and other astronomers discovered some strange things after discovering quasars in 1963. These bright beacons are now considered as hot disks around supermassive black holes in the center of distant galaxies.
Astronomers can see gaps in the spectrum of quasars everywhere. Some wavelengths of light cannot pass through.
1969, Spitzer and Bashir realized what was happening: the lost light was absorbed by the gas at the edge of the galaxy, which was later called the surrounding medium (CGM). Astronomers have been observing quasars, which emit light through the surrounding medium (CGM), just like car lights passing through fog.
However, there was nothing to do at that time. The earth's atmosphere also absorbs light with the same wavelength, so it is difficult to tell which light-blocking atoms are in the surrounding medium (CGM) of the galaxy and which come from the galaxy close to home. Knowing that CGM exists is one thing, and measuring it requires something extra.
Spitzer and Bashir know what they need: a space telescope that can observe from outside the earth's atmosphere.
Bashir never stopped admiring Hubble. In February 2005, he died of a rare blood disease at the age of 70. Six months before his death, he published an article in the Los Angeles Times, urging the US Congress to resume funding the task of repairing some aging Hubble instruments, which was cancelled by NASA after the space shuttle Columbia crashed in 2003.
"This is not only related to a stellar technology, but also to our fundamental pursuit of mankind-our commitment to understanding the universe," Bachir and his colleagues wrote. "Perhaps the most important discovery of Hubble is in the future."
His request was answered: In May 2009, the space shuttle Atlantis repaired the Hubble telescope for astronauts for the last time. During the restoration process, astronauts installed a cosmic origin spectrometer, which can detect the diffused surrounding medium (CGM) gas, and its sensitivity is 30 times higher than that of any previous instrument. Although Hubble's early spectrometers can detect some quasar beams every time, the new equipment allows astronomers to search dozens of galaxies using the light of darker quasars.
A team led by Jason Tumlinson of Baltimore Space Telescope Science Research Institute compiled a catalogue of 44 galaxies from the perspective of Hubble telescope, including a quasar. In a paper published in the journal Science on 20 1 1, the researchers reported that every time they observe a galaxy within 490,000 light years from it, they will see a blank spot in the spectrum covered with light absorbed by atoms. This means that the surrounding medium (CGM) is not unique to several galaxies, they are everywhere.
Tomlinson's team spent the first few years after the Hubble telescope was upgraded. The research team measured the mass and chemical composition of the medium around the galaxy (CGM) and found that they are huge reservoirs of heavy elements. In oxygen alone, the surrounding medium (CGM) contains 654.38+million times the mass of the sun. In many cases, the mass of the surrounding medium (CGM) is equivalent to the mass of the visible part of the whole galaxy.
This discovery provides an answer to a long-standing cosmic mystery: how do galaxies have enough stars to form fuel that lasts for billions of years? Galaxies form stars from collapsed cold gas clouds at a constant rate. For example, the Milky Way produces one or two stars with the mass equivalent to the sun every year. But in the visible part of the galaxy, that is, the disk containing stars, there is not enough cold gas to support the observed star formation rate.
"We think the gas may come from the surrounding medium (CGM)," said Jessica Walker. "But how did the gas enter the galaxy, where did it enter, the time scale of entry, and what prevented it from entering? These are all big problems that keep us awake at night. "
Walker and Pips realized that all these qualities were helpful to solve two other cosmic bookkeeping problems. All elements heavier than helium are formed by nuclear fusion in the center of a star. When stars run out of fuel and explode in the form of supernovae, they will disperse these metals and fold into the next generation of stars.
But if you add all the metals, gases and dust in a star to the disk of a galaxy, it is not enough to explain all the metals that the galaxy has ever made. If we include hydrogen, helium, electrons and protons, which are basically all ordinary substances that should be collected in the Milky Way since the Big Bang, this mismatch will get worse. Astronomers call all these baryons. Galaxies seem to have lost 70% to 95% of their matter.
Therefore, Walker and peebles led a comprehensive work, using Hubble's new spectrometer to calculate all ordinary matter in about 40 galaxies. The researchers published two papers in the 20 14 Journal of Astrophysics.
At that time, Walker reported that at least half of the ordinary matter lost by galaxies could be found in their surrounding medium (CGM). In an update of 20 17, Walker and his colleagues found that the baryon mass in the form of cold gas in the medium around the galaxy (CGM) may be close to 90 billion solar masses. "Obviously, this mass can solve the problem of baryon loss in the Milky Way." The group wrote.
The researchers made a hypothesis about where the missing materials should be and made a prediction. The team tested these predictions through observation and found what they wanted.
In another study, peebles found that although metals were born in the astrolabe of galaxies, they did not stay there. Only 20% to 25% of the metals produced by galaxies remain in stars, gases and dust, and these metals can be incorporated into new stars and planets. The rest may end up in the surrounding medium (CGM).
Tomlinson said: "If you look at all the metals produced by galaxies in their lifetime, they are more outside the galaxy than still inside the Milky Way, which is a huge impact."
Recycling center.
So how does the metal enter the surrounding medium (CGM)? The spectrum of quasars is not helpful to this problem. Their light shows that only one fragment passes through one galaxy at a time. But astronomers can track the growth and development of galaxies through computer simulation according to the physical rules of the behavior of stars and gases.
This strategy reveals the nature of gas agitation and change in the medium around the galaxy (CGM). Simulation studies such as "Evolution and Assembly of Galaxies and Their Environment" initiated by Leiden University in the Netherlands show that metals can reach the surrounding media through the violent life of stars: blowing away a large number of young stars in the powerful radiation wind and spraying metals in the dying struggle of supernovae.
However, once metals enter the surrounding medium (CGM), they do not always remain the same. In the simulation, galaxies seem to use the same gas repeatedly.
"It's basically just gravity." Pips said, "Throw the baseball on it and it will return to the ground." The same is true of gas flowing out of galaxies: unless the gas moves fast enough, it can escape the gravitational limit of galaxies. Otherwise, these atoms will eventually return to the galaxy and form new stars. "
Some simulations show that discrete gas packets propagate from the galactic disk to the surrounding medium (CGM) and then return several times. Surrounding media (CGM) and their galaxies are huge recycling devices.
This means that the atoms that make up planets, plants and humans may have entered the Milky Way many times before they became part of us. In hundreds of millions of years, the atoms that eventually become part of you have traveled hundreds of thousands of light years.
"This is my favorite thing," Tomlinson said. "To some extent, your carbon, oxygen, nitrogen and iron are all in intergalactic space."
How galaxies die out.
However, not all galaxies can retrieve the dielectric gas around them. Losing gas may stop the formation of stars in galaxies forever. No one knows how the formation of stars stopped. But the answer may be in the surrounding medium (CGM).
There are two main forms of galaxies: young spiral galaxies that are forming stars and ancient galaxies that are dying stars.
Tomlinson said: "How galaxies are extinguished and why they remain in this state is one of the most important problems in the process of galaxy formation. This is only related to gas supply. "
Using the light emitted by quasars, researchers can "see" CGM. In this example, the spectra from two galaxies G 1 and G2 lack some wavelengths of light absorbed by CGM atoms (red, in the box at the bottom).
A previously published paper raised the possibility that gas jets heated by supernovae might be stripped from galaxies. Chad Bustard, a physicist at the University of Wisconsin-Madison, and his colleagues simulated the satellite galaxies, the large Magellanic Cloud of the Milky Way, and found that the gas flowing out of this small galaxy was swept away by the slight pressure of the movement around the Milky Way.
Or, the gas in the medium around the dead galaxy (CGM) may be too hot to sink into the galaxy to form stars. If so, the star-formed galaxy should have a surrounding medium (CGM) filled with cold gas, while the dead galaxy should be covered with hot gas. Hot air will float above the galactic disk like a hot air balloon, which is too buoyant to sink to form a star.
But Hubble saw the opposite. There is a lot of oxygen VI—— in the galaxy formed by stars-meaning that the gas is very hot (/kloc-0.00000 degrees Celsius or higher), and the oxygen atom loses its original five electrons. The oxygen content of death galaxies is surprisingly low.
In 20 16, Benjamin Oppenheimer, a computational astrophysicist at the University of Colorado at Boulder, proposed a solution: the "dead" galaxy was not deprived of oxygen at all. The gas is too hot for Hubble to observe. In fact, there is even more oxygen around these passive galaxies.
All these hot gases may explain the death of these galaxies, but these galaxies are also filled with cold gases formed by stars.
Tomlinson said: "There is enough fuel in the fuel tank of the death galaxy. We don't know why they don't use it. Everyone is chasing this problem. "
Until recently, observers were unable to map the surrounding medium (CGM) of a single galaxy. Researchers must add up dozens of quasar beams in order to have an average understanding of their composition.
Teams using two new spectrometers-Keck Cosmic Network Imager (KCWI) on Keck Telescope in Hawaii and Muse—— on Very Large Telescope in Chile-are competing to change this situation. These instruments are called integrated field-of-view spectrometers, which can read the spectrum of the whole galaxy at the same time. With enough background light, astronomers can now examine the entire surrounding medium (CGM) of a single galaxy. Finally, astronomers have a way to test the theory of how gas circulates inside and outside the galaxy.
The Chilean research team led by Sebastian Lopez, an astronomer from the University of Santiago, Chile, and his colleagues used Muse to observe a small dark galaxy, which happened to be sandwiched between a bright, distant galaxy and a large galaxy group closer to the Earth. As a gravitational lens, galaxy cluster distorts the image of distant galaxies into a long and bright arc. The light emitted by this arc passes through the medium around the sandwich galaxy (CGM) at 56 different points (called G 1 by the team).
Surprisingly, the CGM of G 1 is not stable and smooth as expected. Lopez said: "People always think that gas is evenly distributed in every system. This is not the case. "
The light from the source galaxy is deflected and amplified by the middle galaxy cluster, forming a bright arc seen in the rightmost projection image. Different from the narrow beam of quasars, the wide arc illuminates the CGM of most galaxies G 1, showing surprising details.
Meanwhile, peebles's team is re-studying how computers present the surrounding media (CGM). She said: "In the simulation, the resolution of the ring galaxy medium is very poor. Existing simulations well match the visible properties of galaxies-their stars, the gas between stars, and the overall shape and size. But they can't reproduce the characteristics of the galactic medium at all. "
Therefore, she is running a new simulation program called FOGGIE, which pays attention to the surrounding media for the first time. "We found that it changed everything," she said. "The shape, the history of star formation, and even the direction of the Milky Way in space look different."
In short, new observations and simulations show that the role of surrounding media in the life cycle of galaxies is underestimated. Theorists such as peebles and observers such as Omira are cooperating to make new predictions about the appearance of surrounding media. Then, the researchers will check the real galaxies to see if they match.
Although the future research on the Milky Way will focus on collecting spectra from the complete surrounding medium, Tomlinson hopes that he can extract more information from the Hubble telescope now. Hubble telescope makes it possible to study the surrounding medium, but this telescope has been used for 28 years, and there may be less than 10 years left. Hubble telescope is still the best tool to observe some atoms in the surrounding medium, which helps to reveal the secret of gaseous halo.