Alex Knapp

Alex Knapp, Forbes Staff


9/24/2012 @ 1:21PM |7,476 views

Astronomers Discover A Halo Surrounding The Galaxy

Scientists at the Chandra X-Ray Observatory have discovered that our galaxy is surrounded by a halo of hot gasses. If confirmed, this could solve a major physics mystery.

Astronomers working with NASA’s Chandra X-Ray Observatory have detected what they believe is a “halo” of extremely hot gasses surrounding our own Milky Way Galaxy. The gaseous area is huge – stretching out with about a 100 kiloparsec radius. In other words, it’s over 650,000 light years across - which is about 6 times the diameter of the Milky Way.

Previous studies have already discovered a “warm mass” halo around the Galaxy, but this new find demonstrates that there’s a whole other halo – hotter and much more massive. The gasses found within the halo are extremely hot – the astronomers estimate that the temperatures are about 1 million Kelvin, or about 1.8 million degrees Farenheit. There’s also a lot in the gas. The astronomers estimate that the halo contains the mass of over 100 billion Suns. Which is about the same mass as our own Milky Way galaxy.

“Our work shows that, for reasonable values of parameters and with reasonable assumptions, the Chandra observations imply a huge reservoir of hot gas around the Milky Way,” said co-author Smita Mathur in a press release. “It may extend for a few hundred thousand light-years around the Milky Way or it may extend farther into the surrounding local group of galaxies. Either way, its mass appears to be very large.”

That high level of mass, apart from being intrinsically cool,  also provides the potential to solve a major mystery in physics: the “missing baryon” problem.

Baryons are the subatomic particles responsible for over 99% of the mass in the universe. (The protons and neutrons in every atom are baryons.) They’re pretty well understood, but there’s one weird puzzle about them. Based on observations from the Wilkinson Microwave Anisotropy Probe and other instruments, astronomers know what the density of baryons in the universe is. But attempts to count those baryons has only yielded about half the baryons that scientists know exist.

However, if this hot halo of gasses is confirmed, it would account for virtually all of the missing baryons from the Milky Way. Assuming that other galaxies of similar hot halos, this discovery could pave the way for solving what for over a decade has been a perplexing problem.

This is only a preliminary finding. And there’s still a lot of work to be done when it comes to understanding both the halo and its astronomical implications. But it’s an exciting one that, if confirmed, gives astronomers a big leg up in understanding the makeup of the universe.

(Image Credit: NASA/CXC/M.Weiss)


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  • So, this is crazy cool, but…..

    How is heat loss not occuring here? How is it held together? How is the gas not combusting? How is the interior of the galaxy generally so cool with this truly massive source of energy surrounding it?

  • Fill Fill Fill Fill 1 year ago

    Good questions. I’d like to comment on a couple of them:

    “How is it held together?”

    Probably just gravity. And where else would it go?

    “How is the gas not combusting?”

    It probably simply isn’t dense enough. For something to combust, it needs to be flammable and oxygen needs to be present. That said, what’s to say it didn’t combust? You’d still have a gas, like carbon dioxide and/or water vapor.

  • Yeah, those make sense- especially about density. In a very low-pressure environment at very high temperatures, density would be quite low.

    Of course, doesn’t that make the heat even more puzzling? It does to me, anyway- anyway, I’ll await for a smarter physicist to explain this to me.

  • Alex Knapp Alex Knapp, Forbes Staff 1 year ago

    The heat comes from the fact that even though it’s mostly a bunch of hydrogen, it’s spinning very quickly – which means that they keep running into each other – which generates heat.

  • Ah- makes sense- same thing that *might* be creating enough energy to keep water liquefied in some of the moons around the larger planets, right?

  • Roz Bennetts Roz Bennetts 1 year ago

    Great discovery!

  • Fill Fill Fill Fill 1 year ago

    I wonder how this relates to Dark Matter?

  • Alex Knapp Alex Knapp, Forbes Staff 1 year ago

    Probably not much – the missing baryon problem is just that the measured density of baryons in the universe is twice as much as we’ve counted. But if these halos are around other gasses, it makes up for that missing matter – but consistent with the measured density.

  • Fill Fill Fill Fill 1 year ago

    Right, they are separate. But, I would suppose that the gravity by the dark matter is a strong reason why the gas is out there and not ‘fallen in’ to the galaxy? For the same reason why the galaxy rotates nearly uniformly because of the dark matter gravity’s influence. It also might have something to do with why the gas is hot, too, because it is moving very quickly being so far out from the center of the universe (the same way gas gets superheated as it falls into a black hole).

  • Alex Knapp Alex Knapp, Forbes Staff 1 year ago

    I think that’s a pretty reasonable supposition.