Milky Way’s Halo Is Clumpy And Into Recycling

KEY POINTS

  • The Milky Way is surrounded by a halo of hot gas
  • Researchers used data from a tiny satellite that has been observing the galaxy’s halo
  • The researchers found stronger X-rays in parts with more star formation
  • Studying the halo could shed light on the mystery of the Universe’s missing baryonic matter

Our galaxy has a halo of hot gases around it and a team of researchers found that it’s actually into recycling. What could this mean about the mystery of the universe’s missing baryonic matter?

The Milky Way, just like most disk and elliptical galaxies, is surrounded by what’s known as a “circumgalactic medium” or a halo of hot gas. Our nearby neighbor, the Andromeda galaxy, also has this halo. And only recently, a team of researchers found that Andromeda’s halo is actually so massive that it already touches the Milky Way’s.

In a new study funded by NASA’s Astrophysics Division, a team of astronomers discovered that the Milky Way’s halo is actually “clumpy” and, that the galaxy may actually be supplying it with recycled materials from star activity.

For the study, the researchers used the observations of HaloSat, a 4 by 8 by 12 inches mini satellite and was first launched from the International Space Station (ISS) in 2018. Based on the tiny satellite’s observations of the halo, the researchers determined that the Milky Way’s halo has a “disk-like geometry,” with the X-ray emissions being stronger in the parts where there is more star formation, corresponding author Professor Philip Kaaret of the University of Iowa (UI) said in the UI news release.

“That suggests the circumgalactic medium is related to star formation, and it is likely we are seeing gas that previously fell into the Milky Way, made stars, and now is being recycled into the circumgalactic medium,” Kaaret added.

Milky Way A Hubble telescope edge-on view of the ESO 510-G13 galaxy is seen in this undated NASA photograph. The image shows the galaxy”s warped dusty disk and shows how colliding galaxies spawn the formation of new generations of stars. The dust and spiral arms of normal spiral galaxies, like our own Milky Way, appear flat when viewed edge-on. Photo: Getty Images/NASA

Why does this matter? This is because learning more about the Milky Way’s halo could, in turn, also shed light on a much bigger mystery in the universe. 

The team actually wanted to determine how massive the Milky Way’s halo is, specifically whether it’s many times the size of the galaxy. If it is, then it could provide clues about the baryonic matter that’s been believed to be missing since the universe was born.

“If it’s a huge, extended halo that is many times the size of our galaxy, it could house enough material to solve the missing baryon question,” a NASA news release on the study said.

On the other hand, if the halo turns out to be composed mostly of the recycled material, then it’s unlikely to be hosting the missing baryonic matter, the UI

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The Milky Way galaxy has a clumpy halo

The Milky Way galaxy has a clumpy halo
A mini satellite designed and built at the University of Iowa has determined the Milky Way galaxy is surrounded by a heated, clumpy halo of gas that is continually being supplied by birthing or dying stars in our galaxy. Credit: Blue Canyon Technologies

The Milky Way galaxy is in the recycling business.


University of Iowa astronomers have determined our galaxy is surrounded by a clumpy halo of hot gases that is continually being supplied with material ejected by birthing or dying stars. This heated halo, called the circumgalactic medium (CGM), was the incubator for the Milky Way’s formation some 10 billion years ago and could be where basic matter unaccounted for since the birth of the universe may reside.

The findings come from observations made by HaloSat, one of a class of minisatellites designed and built at Iowa—this one primed to look at the X-rays emitted by the CGM. The researchers conclude the CGM has a disk-like geometry, based on the intensity of X-ray emissions coming from it. The HaloSat minisatellite was launched from the International Space Station in May 2018 and is the first minisatellite funded by NASA’s Astrophysics Division.

“Where the Milky Way is forming stars more vigorously, there are more X-ray emissions from the circumgalactic medium,” says Philip Kaaret, professor in the Iowa Department of Physics and Astronomy and corresponding author on the study, published online in the journal Nature Astronomy. “That suggests the circumgalactic medium is related to star formation, and it is likely we are seeing gas that previously fell into the Milky Way, helped make stars, and now is being recycled into the circumgalactic medium.”

Each galaxy has a CGM, and these regions are crucial to understanding not only how galaxies formed and evolved but also how the universe progressed from a kernel of helium and hydrogen to a cosmological expanse teeming with stars, planets, comets, and all other sorts of celestial constituents.

HaloSat was launched into space in 2018 to search for atomic remnants called baryonic matter believed to be missing since the universe’s birth nearly 14 billion years ago. The satellite has been observing the Milky Way’s CGM for evidence the leftover baryonic matter may reside there.

To do that, Kaaret and his team wanted to get a better handle on the CGM’s configuration.

More specifically, the researchers wanted to find out if the CGM is a huge, extended halo that is many times the size of our galaxy—in which case, it could house the total number of atoms to solve the missing baryon question. But if the CGM is mostly comprised of recycled material, it would be a relatively thin, puffy layer of gas and an unlikely host of the missing baryonic matter.

“What we’ve done is definitely show that there’s a high-density part of the CGM that’s bright in X-rays, that makes lots of X-ray emissions,” Kaaret says. “But there still could be a really big, extended halo that is just dim in X-rays. And it might be harder

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