Spiral galaxies like Milky Way bigger than thought, study finds

Jun 27, 2013
Spiral galaxies like Milky Way bigger than thought, says CU-Boulder study
A new CU-Boulder study indicates spiral galaxies like our Milky Way, and the M74 Galaxy shown here, are larger and more massive than previously believed. Credit: NASA

Let's all fist bump: Spiral galaxies like our own Milky Way appear to be much larger and more massive than previously believed, according to a new University of Colorado Boulder study by researchers using the Hubble Space Telescope.

CU-Boulder Professor John Stocke, study leader, said new observations with Hubble's $70 million Cosmic Origins Spectrograph, or COS, designed by CU-Boulder show that normal spiral galaxies are surrounded by halos of gas that can extend to over 1 million light-years in diameter. The current estimated diameter of the Milky Way, for example, is about 100,000 light-years. One light-year is roughly 6 trillion miles.

The material for galaxy halos detected by the CU-Boulder team originally was ejected from galaxies by exploding stars known as supernovae, a product of the star formation process, said Stocke of CU-Boulder's astrophysical and planetary sciences department. "This gas is stored and then recycled through an extended galaxy halo, falling back onto the galaxies to reinvigorate a new generation of star formation," he said. "In many ways this is the 'missing link' in galaxy evolution that we need to understand in detail in order to have a complete picture of the process."

Stocke gave a presentation on the research June 27 at the University of Edinburgh's Higgs Centre for Theoretical Physics in Scotland at a conference titled "Intergalactic Interactions." The CU-Boulder research team also included professors Michael Shull and James Green and research associates Brian Keeney, Charles Danforth, David Syphers and Cynthia Froning, as well as University of Wisconsin-Madison Professor Blair Savage.

Building on earlier studies identifying oxygen-rich gas clouds around spiral galaxies by scientists at the Space Telescope Science Institute in Baltimore, the University of Massachusetts, Amherst College and the University of California, Santa Cruz, Stocke and his colleagues determined that such clouds contain almost as much mass as all the stars in their respective galaxies. "This was a big surprise," said Stocke. "The new findings have significant consequences for how spiral galaxies change over time."

In addition, the CU-Boulder team discovered giant reservoirs of gas estimated to be millions of degrees Fahrenheit that were enshrouding the spiral galaxies and halos under study. The halos of the spiral galaxies were relatively cool by comparison—just tens of thousands of degrees—said Stocke, also a member of CU-Boulder's Center for Astrophysics and Space Astronomy, or CASA.

Shull, a professor in CU-Boulder's astrophysical and planetary sciences department and a member of CASA, emphasized that the study of such "circumgalactic" gas is in its infancy. "But given the expected lifetime of COS on Hubble, perhaps another five years, it should be possible to confirm these early detections, elaborate on the results and scan other spiral galaxies in the universe," he said.

Prior to the installation of COS on Hubble during NASA's final servicing mission in May 2009, theoretical studies showed that spiral galaxies should possess about five times more gas than was being detected by astronomers. The new observations with the extremely sensitive COS are now much more in line with the theories, said Stocke.

The CU-Boulder team used distant quasars—the swirling centers of supermassive black holes—as "flashlights" to track ultraviolet light as it passed through the extended gas haloes of foreground galaxies, said Stocke. The light absorbed by the gas was broken down by the spectrograph, much like a prism does, into characteristic color "fingerprints" that revealed temperatures, densities, velocities, distances and chemical compositions of the gas clouds.

"This is way too diffuse to allow its detection by direct imaging, so spectroscopy is the way to go," said Stocke. CU-Boulder's Green led the design team for COS, which was built by Ball Aerospace & Technologies Corp. of Boulder for NASA.

While astronomers hope the Hubble Space Telescope keeps on chugging for years to come, there will be no more servicing missions. And the James Webb Space Telescope, touted to be Hubble's successor beginning in late 2018, has no UV light-gathering capabilities, which will prevent astronomers from undertaking studies like those done with COS, said Green.

"Once Hubble ceases to function, we will lose the capability to study galaxy halos for perhaps a full generation of astronomers," said Stocke. "But for now, we are fortunate to have both Hubble and its Cosmic Origins Spectrograph to help us answer some of the most pressing issues in cosmology."

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User comments : 10

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GSwift7
5 / 5 (7) Jun 27, 2013
The title says "bigger than thought", but this observation was actually expected. The COS instrument was built because the theory predicted this, and they wanted to either confirm or deny it. So as it turns out, the title should have been something more like 'spiral galaxies like milky way are as big as expected, study finds'.

I also wouldn't be surprised if they adjust the numbers upwards once they get more data. This is probably a conservative interpretation of the numbers.
cantdrive85
1.3 / 5 (13) Jun 27, 2013
Hot gas! Except that it isn't.
thermodynamics
4.4 / 5 (7) Jun 27, 2013
Cantdrive85 said:
Hot gas! Except that it isn't.


Please give us links to the data that supports this assertion? Please show us how you have come to a conclusion that no astronomers have?
cantdrive85
1.3 / 5 (14) Jun 27, 2013
Why give you links when it's right there in the article.

In addition, the CU-Boulder team discovered giant reservoirs of gas estimated to be millions of degrees Fahrenheit that were enshrouding the spiral galaxies and halos under study. The halos of the spiral galaxies were relatively cool by comparison—just tens of thousands of degrees—said Stocke, also a member of CU-Boulder's Center for Astrophysics and Space Astronomy, or CASA.


Yep, no gas to be found just plasma. How can I arrive at that conclusion while astrophysicists haven't? Ignorance on their part, I suppose.
GSwift7
5 / 5 (11) Jun 27, 2013
Yep, no gas to be found just plasma. How can I arrive at that conclusion while astrophysicists haven't? Ignorance on their part, I suppose


It must be nice to go through life being so oblivious, with a child-like simplistic view of the world around you, completely unaware of the complexities underlying the trivialities you grasp to.

The 'temperatures' they mention are the average speed of the molecules and atoms. In reality the material is a range of different things, from solids to liquids to gases to plasmas. The temperatures of individual particles will range from near zero to double the nubers shown above. They could have said ice, dust, gas and plasma, but they decided to just simplify it so that readers can get the idea. Anyone who cares can look up the actual composition on thier own. You should try that. Go read about it before you continue to rant about your own ignorance.
cantdrive85
1 / 5 (13) Jun 27, 2013
They could have said ice, dust, gas and plasma, but they decided to just simplify it so that readers can get the idea.

Here I thought I was doing the same, a vast mixture of materials that behave like plasma. But I guess your simplistic view only applies to your own POV.
xX_GT_Xx
1 / 5 (6) Jun 27, 2013
"Stocke and his colleagues determined that such clouds contain almost as much mass as all the stars in their respective galaxies"

So this *doubles* the expected mass of the galaxies, and expands their diameter by a factor of 10? Anyone going to factor that in to stellar motion, galactic rotation, lensing magnitude, etc, all the apparent discrepancies that get the "dark matter" non-answer slapped on them?
GSwift7
5 / 5 (4) Jun 27, 2013
Here I thought I was doing the same, a vast mixture of materials that behave like plasma. But I guess your simplistic view only applies to your own POV


No, you said there's no gas, implying that it is all plasma, which is wrong, and only the plasma portion will act as plasma.

So this *doubles* the expected mass of the galaxies, and expands their diameter by a factor of 10?


Not exactly. The stars only make up a portion of the visible mass in a galaxy. Big nebulae can have the mass of 10's of thousands of stars. I don't think they have doubled the visible mass of the galaxy as a whole. This doesn't change the total mass at all. This just verifies the existence of the halo we theorized.

We have assumed that something like this was there, but we just couldn't see it. It doesn't change the amount of dark matter, since this halo was already calculated into it. It is another confirmation that our theory is on the right track, and some kind of dark mass is still there.
Grallen
not rated yet Jun 28, 2013
I suppose this helps explain the motion of stars in spiral galaxies a little better. I can't wait to see more details.

Does this lower the mass needed in the central black hole in gravitational models?

I wonder how much more gas is out there that we can't see yet.
Fleetfoot
5 / 5 (2) Jun 28, 2013
I suppose this helps explain the motion of stars in spiral galaxies a little better. I can't wait to see more details.

Does this lower the mass needed in the central black hole in gravitational models?


No, the mass of the SMBH is a small fraction of the total. The mass of Sag A* for example is measured using the orbits of corse stars which orbit it so this is irrelevant.

It would slightly change the ratio of dark matter to visible in estimates that haven't previously used the correct value, but as has been said, this result was expected.