Cosmic 'leaf blower' robs galaxy of star-making fuel

Apr 04, 2012 By Adam Hadhazy
Time is running out for the galaxy NGC 3801, seen in this composite image combining light from across the spectrum, ranging from ultraviolet to radio. NASA's Galaxy Evolution Explorer and other instruments have helped catch the galaxy NGC 3801 in the act of destroying its cold, gaseous fuel for new stars. Astronomers believe this marks the beginning of its transition from a vigorous spiral galaxy to a quiescent elliptical galaxy whose star-forming days are long past. Credit: NASA/JPL-Caltech/SDSS/NRAO/ASIAA

(PhysOrg.com) -- Supernova explosions and the jets of a monstrous black hole are scattering a galaxy's star-making gas like a cosmic leaf blower, a new study finds. The findings, which relied on ultraviolet observations from NASA's Galaxy Evolution Explorer and a host of other instruments, fill an important gap in the current understanding of galactic evolution.

It has long been known that gas-rich spiral galaxies like our Milky Way smash together to create such as the one observed in the study. These big, round galaxies have very little star formation. The reddish glow of aging stars comes to dominate the complexion of elliptical galaxies, so astronomers refer to them as "red and dead."

The process that drives the dramatic transformation from spiral galactic youth to elderly elliptical is the rapid loss of cool gas, the fuel from which form. Supernova explosions can start the decline in star formation, and then from the finish the job. Now astronomers think they have identified a recently merged galaxy where this gas loss has just gotten underway.

"We have caught a galaxy in the act of destroying its gaseous fuel for new stars and marching toward being a red-and-dead type of galaxy," said Ananda Hota, lead author of a new paper in the . Hota, an astronomer in Pune, India, conducted the study as a post-doctoral research fellow at the Institute of Astronomy & Astrophysics at Academia Sinica in Taipei, Taiwan.

"We have found a crucial missing piece to connect and solve the puzzle of this phase of ," Hota added.

The supermassive that reside in the centers of galaxies can flare up when engorged by gas during galactic mergers. As a giant black hole feeds, colossal jets of matter shoot out from it, giving rise to what is known as an active galactic nucleus. According to theory, shock waves from these jets heat up and disperse the reservoirs of cold gas in elliptical galaxies, thus preventing new stars from taking shape.    

Astronomers believe they have caught the galaxy NGC 3810 at a critical point in its history, just as it is making the transition from a vigorous spiral galaxy to a quiescent elliptical galaxy whose star-forming days are long past. This diagram sketches out the stages leading up to its current observed state and beyond. Credit: NASA/JPL-Caltech

The galaxy Hota and his team looked at, called NGC 3801, shows signs of such a process. NGC 3801 is unique in that evidence of a past merger is clearly seen, and the shock waves from the central black hole's jets have started to spread out very recently. The researchers used the to determine the age of the galaxy's stars and decipher its evolutionary history. The ultraviolet observations show that NGC 3801's star formation has petered out over the last 100 to 500 million years, demonstrating that the galaxy has indeed begun to leave behind its youthful years. The lack of many big, new, blue stars makes NGC 3801 look yellowish and reddish in visible light, and thus middle-aged.

What's causing the galaxy to age and make fewer stars? The short-lived blue stars that formed right after it merged with another galaxy have already blown up as supernovae. Data from NASA's Hubble Space Telescope revealed that those stellar explosions have triggered a fast outflow of heated gas from NGC 3801's central regions. That outflow has begun to banish the reserves of cold gas, and thus cut into NGC 3801's overall star making.

Some star formation is still happening in NGC 3801, as shown in ultraviolet wavelengths observed by the Galaxy Evolution Explorer, and in infrared wavelengths detected by NASA's Spitzer Space Telescope. But that last flicker of youth will soon be extinguished by colossal shock waves from the black hole's jets, seen in X-ray light by NASA's Chandra X-ray Observatory. These blast waves are rushing outward from the galactic center at a velocity of nearly two million miles per hour (nearly 900 kilometers per second). The waves will reach the outer portions of NGC 3801 in about 10 million years, scattering any remaining cool hydrogen gas and rendering the galaxy truly red and dead.

Astronomers think the transition captured early-on in the case of NGC 3801 -- from the merger of gas-rich to the rise of an old-looking elliptical -- happens very quickly on cosmic time scales.

"The quenching of by feedback from the active galactic nucleus probably occurs in just a billion years. That's not very long compared to the 10-billion-year age of a typical big galaxy," said Hota. "The explosive shock wave event caused by the central black hole is so powerful that it can dramatically change the future course of the evolution of an entire galaxy."

Additional observations for the study in optical light come from the Sloan Digital Sky Survey and in radio using the Very Large Array in New Mexico.

Other authors of the paper include Soo-Chang Rey, Suk Kim and Jiwon Chung of Chungnam National University, Daejeon, Republic of Korea; Yongbeom Kang, also of Chungnam National University and Johns Hopkins University, Baltimore, Md.; and Satoki Matsushita, also of the Academia Sinica Institute of Astronomy and Astrophysics, Taipei, Taiwan.

Explore further: 'Blockbuster' science images

Related Stories

NGC 4696: A cosmic question mark

Aug 12, 2010

This picture, taken by Hubble's Advanced Camera for Surveys, is not just a beautiful snapshot of NGC 4696, the largest galaxy in the Centaurus Cluster (galaxy cluster Abell 3526). It is also an illustration ...

Classic portrait of a barred spiral galaxy

Feb 03, 2012

(PhysOrg.com) -- The NASA/ESA Hubble Space Telescope has taken a picture of the barred spiral galaxy NGC 1073, which is found in the constellation of Cetus (The Sea Monster). Our own galaxy, the Milky Way, ...

Chandra finds nearest pair of supermassive black holes

Aug 31, 2011

(PhysOrg.com) -- Astronomers have used NASA's Chandra X-ray Observatory to discover the first pair of supermassive black holes in a spiral galaxy similar to the Milky Way. At a distance of 160 million light ...

Image: Active Galaxy Centaurus A

Jan 04, 2012

(PhysOrg.com) -- Resembling looming rain clouds on a stormy day, dark lanes of dust crisscross the giant elliptical galaxy Centaurus A.

Recommended for you

'Blockbuster' science images

Nov 21, 2014

At this point, the blockbuster movie Interstellar has created such a stir that one would almost have to be inside a black hole not to know about it. And while the science fiction thriller may have taken some ...

Estimating the magnetic field of an exoplanet

Nov 20, 2014

Scientists developed a new method which allows to estimate the magnetic field of a distant exoplanet, i.e., a planet, which is located outside the Solar system and orbits a different star. Moreover, they ...

It's filamentary: How galaxies evolve in the cosmic web

Nov 20, 2014

How do galaxies like our Milky Way form, and just how do they evolve? Are galaxies affected by their surrounding environment? An international team of researchers, led by astronomers at the University of ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

Tuxford
1 / 5 (2) Apr 05, 2012
The opening line should read, "It has long been assumed...." So many assumptions are stated as fact in this article that it must be discounted as comic. It has long been assumed that giant ellipticals are formed by mergers, with strikingly little observational evidence.

Far more likely is that the active galactic nuclei eruptions have grown so frequent and severe that the stars are migrating outward, with fewer new ones forming in the central turbulent region. Here is the scenario, as I stated in my first post on this board. And since that post, I have found little counter-evidence. In fact, the evidence, correctly interpreted, seems to support this 'continuous creation' evolutionary model.

http://www.physor...ars.html

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.