A team of researchers used Mauna Kea Observatory's Keck telescope to examine a seemingly empty region of the sky to reveal the invisible gas that covers all galaxies in the universe. The researchers a Astronomy Nature The first detailed data on a gaseous halo extending 100,000 light-years into space has been published. If the Milky Way also has a similar halo, it is likely already interacting with the halo of our galactic neighbor, Andromeda.
Most of the matter in the universe is not made up of the bright stars we see in beautiful pictures of galaxies. Stellar cities are surrounded by dark matter, which some researchers believe is made up of strange, invisible particles. But even most of the normal matter is found not in stars, but in the vast clouds of gas that surround galaxies.
According to the research team, galactic halos can contain up to 70-90% of the universe’s normal matter: mainly hydrogen, helium, carbon, nitrogen and oxygen. This diffuse gas is the birthplace of all stars and planets. By learning about it, we can also learn more about our past.
Gas halos cover a large area, so they are very faint. They are tens or even a hundred thousand times fainter than the bright parts of the galaxy. We have known about their existence since the 1950s. Astronomers then discovered that certain regions absorb certain frequencies of electromagnetic radiation. However, these measurements provide only one point of information about parts of space hundreds or thousands of light-years across, so we know very little about the exact size and shape of halos, or how gas flows between them and the galaxy.
For a long time, researchers believed that it was impossible to take pictures of the halos themselves, but that changed with the development of a new type of spectrograph, the image splitter. This tool allows us to take spectra of the faintest regions.
Chris Martin (Caltech), a member of the Caltech Research Group, has developed a spectrograph capable of measuring extremely faint targets, the Cosmic Web Imager, which is mounted on one of the world's largest optical telescopes, the Keck Telescope. With this new device, even extremely faint targets can be observed.
The research team observed a seemingly empty part of the sky for an entire night. The data was then subjected to comprehensive analysis to create an image of the halo surrounding one of the galaxies.
The group examined the radiation of hydrogen and oxygen in an area ten times larger than what is traditionally classified as a galaxy. It has been shown that most of the conventional matter in the universe consists of diffuse gas halos. It has also been shown that the galaxy does not simply blend into the surrounding halo. A clear break can be seen at the boundary between the two. There has been much debate about this transition in the past, but the new data clearly shows the edge of the starry part of space.
We still don't know why we can see this gas at all. It's bright, but we don't know why.
We can often see the glow of hydrogen gas in galaxies because it is heated by the intense radiation of surrounding stars. However, outside the galaxy, there are no stars close enough to explain the glow.
One possibility is that the halo is made up of streams of gas moving in different directions. We see the glow when the streams collide at high speed.
It is also possible that some massive stars and some black holes (inside galaxies) emit very strong ultraviolet radiation. Some of this radiation escapes the galaxy and provides a kind of ultraviolet background radiation for the universe.
Together, the fast-moving gas flows and the ultraviolet background may be enough to cause the observed glow, but more observations are needed to be sure.
source: phys.org
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