Upgraded HET Re-dedicated
Upgraded Hobby-Eberly Telescope Sees First Light
Tracking HET’s Progress
VIRUS units come together
News Releases
HETDEX in the News
Image & Media Gallery


This text will be replaced

Fireworks from Colliding Galaxies

When galaxies collide, they produce some of the grandest fireworks displays in the universe. Clouds of gas ram together to create new stars, some of which are so massive that they quickly blast themselves to bits as supernovae.

Three Steps Toward a Galactic Merger

These three interacting systems, viewed by Hubble Space Telescope, are targets for VIXENS. Each system demonstrates a different phase in the process of a galactic merger.

NGC 5257/8

NGC 5257/8, two galaxies that are just beginning the merger process [NASA/ESA/Hubble Heritage Team (STScI/AURA)A.Evans (Univ. Virginia)]

M51, the stunning Whirlpool galaxy, is in the middle stages of a merger. [NASA/ESA/Hubble Heritage Team (STScI/AURA)/S.Beckwith (STScI)]

The two galaxies that make up NGC 6621 are nearing the end of the merger process. [NASA/ESA/Hubble Heritage Team (STScI/AURA)W.Keel (Univ. Alabama, Tuscaloosa)]

University of Texas graduate student Amanda Heiderman is using VIRUS-P to study these pyrotechnics. Her project, known as VIXENS (VIRUS-P Investigation of the eXtreme Environments of Starbursts), is targeting 20 systems of colliding galaxies, from those that are just beginning the process to those that have merged to form a single galaxy. VIXENS will study the process of star formation in these interacting galaxies.

“We call them extreme environments because when two systems collide, gravity [pulls] the gas toward the central regions [of the galaxies] and it piles up,” says Heiderman. “All this gas piled in the center delivers a very, very powerful burst of star formation. And the more gas you have, the more star formation you can have.”

A galactic collision begins as two galaxies pass close to each other. Gravitational interactions between them drive gas from the outer regions of each galaxy toward their centers. As the gas piles up, it may fragment into small clumps that then collapse to form stars.

The interacting galaxies loop around each other several times, further distorting their shapes and triggering more starbirth. After hundreds of millions of years or longer, the galaxies merge, and the rate at which new stars are born intensifies. The merging galaxies may form “starbursts,” where the rate of star formation is thousands of times greater than in more sedate galaxies like the Milky Way, which gives birth to an average of about one star per year.

Over millions of years more, the galaxies complete the merger. They typically form elliptical galaxies, which look like fat, fuzzy rugby balls. The rate of starbirth plunges.

Heiderman is studying all three phases of galactic interaction — initial approach, contact, and merger.

Using VIRUS-P attached to the 107-inch (2.7-meter) Harlan J. Smith Telescope at McDonald Observatory, she can probe each interacting galaxy in detail. VIRUS-P provides a look at many regions within the galaxies, from their edges to their centers, allowing Heiderman to study the process of star formation in each region.

“It can allow us to look at these systems in smaller pieces,” Heiderman says. “When we have a measurement of small-scale star formation, we can begin to connect it with local star formation in our own galaxy, which we can observe on extremely small scales.

“Using VIRUS-P, you can obtain a picture of a whole galaxy, and because of how the instrument is set up, you can look at an individual segment of a galaxy that’s the size of one of VIRUS-P’s 246 fibers. You can position it where you want these little segments, you can gather data in these very small regions, and you can cover the [whole] galaxy.”

Heiderman, along with VIXENS collaborators Neal Evans, Karl Gebhardt, Casey Papovich, and Guillermo Blanc, began her observations in May 2009, and data collection and analysis will continue well into 2010. In addition, she will compare her results to those from two other ground-based telescopes and two space-based telescopes — Spitzer Space Telescope, which observes the infrared sky, and the Galaxy Evolution Explorer, which observes ultraviolet wavelengths. The different wavelengths provide information on star formation in the target galaxies.

Comparing the data from the different telescopes will tell the collaborators if there is a relationship for the different galaxies and allow them to compare their results with earlier measurements.

Additional Resources

VIXENS webpage