Our Milky Way galaxy is surrounded by a hot halo, scientists say

Our galaxies is surrounded by a halo that is much hotter than scientists previously thought, according to new research.

What's more, other galaxies could be wrapped in the same hot ring.

Scientists had already found that the halo, which is made up of dust, gas and dark matter that is wrapped around our galaxy, was at least 10 times hotter than had known before. But there was nothing to suggest that one measurement was not simply just an especially warm part of the halo, rather than an indication of conditions elsewhere.

Now new research suggests those extreme temperatures might actually be found right across the entire halo, and could be found in similar places around other galaxies.

"We can't say for sure that it is everywhere, because we have not analyzed the entire halo," said ​Smita Mathur, professor of astronomy at Ohio State. "But we know now that the temperatures we saw in the first study definitely are not unique, and that is very exciting."

The new findings could help researchers understand the halos, as well as how they and the galaxies they surround are formed. The halo marks the threshold between our Milky Way and the wider universe, and so could help offer clues about how galaxies grow and change.

"We are trying to learn about the elements that form these halos, and about the temperatures there," she said.

"Knowing those things can help us understand more about how galaxies connect with the rest of the universe, and how they formed and where elements might have come from."

Researchers initially measured the heat of the halo by looking through the XMM-Newton telescope, which is run by the European Space Agency and collects X-rays that would otherwise have been blocked by Earth's atmosphere.

That data focused on one particular direction within the Milky Way – showing that the halo there was much hotter than expected, but not whether it would be the case elsewhere.

"It showed us that the halo was much hotter than we had known, but it didn't show us whether that was the case throughout the galaxy, or if the telescope had picked up an aberration caused by an unknown force coming from the direction where the telescope was pointed," said Mathur, who was the senior researcher on the trio of studies, which were presented this week at the online meeting of the American Astronomical Society.

The researchers then used a Japanese X-ray telescope called Suzaku, which collected data from the Milky Way's halo by looking in four different directions. As well as confirming the earlier findings about the heat of the universe, they also showed that other parts of the halo are likely to be as hot too.

Researchers also looked at data from another galaxy known as NGC 3221, which is 200 million light years away but is similar in shape and size to the Milky Way. That research indicated that galaxy's halo is about as hot as our own.