Newswise — AMHERST, Mass. – New, high-precision equipment orbiting Earth aboard
the Hubble Space Telescope is now sending such rich data back to astronomers,
some feel they are crossing the final frontier toward understanding galaxy
evolution, says Todd Tripp, leader of the team at the University of
Massachusetts Amherst.
Galaxies are the birthplaces of stars, each with a
dense, visible central core and a huge envelope, or halo, around it containing
extremely low-density gases. Until now, most of the mass in the envelope, as
much as 90 percent of all mass in a galaxy, was undetectable by any instrument
on Earth.
But Hubble’s sensitive new Cosmic Origins Spectrograph (COS),
the only one of its kind, has dramatically improved the quality of information
regarding the gaseous envelope of galaxies, Tripp says. This huge gain in
precision is one of the enormous accomplishments of the COS mission. “Even 10
years ago, most of the mass of a galaxy was invisible to us and such detailed
investigations were impossible,” the UMass Amherst astronomer points out. “With
COS, in a sense we now have the ability to see the rest of the iceberg, not just
the tip. This is a very exciting time to be an astronomer.”
Tripp,
postdoctoral researcher Joe Meiring and theoretical astronomer Neil Katz are
co-authors of several companion articles reporting advances in understanding
galaxy evolution based on the new COS data in the Nov. 18 issue of Science.
Other lead investigators are Nicolas Lehner of the University of Notre Dame and
Jason Tumlinson of the Space Telescope Science Institute,
Baltimore.
“With the new spectrograph we can see galaxy halos out to at
least 150,000 parsecs,” says Tripp. One kiloparsec is about 19 trillion miles.
“Where once we saw only the framework we are now getting a more complete
picture, including the composition and movement of gases in the envelope,
varying temperatures in different locations and the chemical structure, all in
incredible detail,” Tripp adds.
In particular, data on the chemical
composition and temperature in the gas clouds allow the astronomers to calculate
a galaxy’s halo mass and how the gaseous envelope regulates the galaxy’s
evolution.
Another overall mission focus is to explore how galaxies
gather mass for making stars. The astronomers have found that heavy elements in
the envelopes surrounding the most vigorous star-forming galaxies continuously
recycle material, as supernovae explode and shoot hot gas for trillions of
miles. Faster-moving material escapes the envelope, but slower-moving particles
collapse back into the center and restart the cycle.
Tripp and his UMass
Amherst team specialize in studying how the fast-moving gases and matter from
exploding supernovae circulate in galaxies. It was a surprise to discover how
much mass extends far outside each galaxy, he says. “Not only have we found that
star-forming galaxies are pervasively surrounded by large halos of hot gas,”
says Tripp, “we have also observed that hot gas in transit. We have caught the
stuff in the process of moving out of a galaxy and into intergalactic
space.”
Further, the speed at which gases are moving in different parts
of a galaxy is critical. Slower speeds may mean cooling gases, ready to collapse
back into the core. Hotter gases are likely expanding and might escape the
envelope.
Because the light emitted by this hot plasma is so faint that
it is effectively invisible, astronomers use a trick to illuminate it from
behind, like studying a misty fog bank by looking through lighthouse beams. In
this case the lighthouse is usually a quasar, a super bright object behind the
galaxy of interest. Gathering several sightings through the fog, scientists can
piece together a map of the gaseous envelope.
Certain wavelengths of
light emitted by the quasar are absorbed by the ions in a galaxy’s envelope.
With COS, a whole new area of the electromagnetic spectrum has become visible.
To learn more, Tripp and colleagues also calculate concentrations of the many
elements such as hydrogen, oxygen, sulfur, carbon and neon in the envelope, plus
up to five ions of each. One of the neon ions has turned out to be particularly
important.
“In detecting the neon ions we find that there’s a lot of gas
at several hundred thousand degrees Kelvin, which we’ve never been able to see
unambiguously before,” says Tripp. “It means we can characterize the total mass
distribution in the envelope, setting more precise constraints on the
temperatures overall. We can now access more diverse ions, and we have new
leverage on determining whether stuff is heating up or cooling off. We’re
gaining new insights.”
The neon ion will also play a role in testing
theoretical models of galaxy evolution. Theorists including Katz at UMass
Amherst construct model galaxies on a computer, simulating its make-up and how
it evolves over time. Tripp says, “Now we have hard data to plug into the model
and test their ideas. They’ve got a lot of detailed predictions we can now
compare to the real universe. It’s a new day for all of us.”
This article was first published at www.newswise.com
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