“Galaxies are complicated, messy beasts, and we think outflows and winds are critical pieces to how they form and evolve, regulating their ability to grow,” said astronomer Justin Spilker at the University of Texas.
For the first time, a powerful “wind” of molecules has been detected in a galaxy located 12 billion light-years away. Probing a time when the universe was less than 10 percent of its current age, University of Texas at Austin astronomer Justin Spilker’s research sheds light on how the earliest galaxies regulated the birth of stars to keep from blowing themselves apart. The research will appear in the Sept. 7 issue of the journal Science.
Some galaxies such as the Milky Way and Andromeda have relatively slow and measured rates of starbirth, with about one new star igniting each year. Other galaxies, known as starburst galaxies (see Antennae galaxies above), forge hundreds or even thousands of stars each year. This furious pace, however, cannot be maintained indefinitely.
To avoid burning out in a short-lived blaze of glory, some galaxies throttle back their runaway starbirth by ejecting — at least temporarily — vast stores of gas into their expansive halos, where the gas either escapes entirely or slowly rains back in on the galaxy, triggering future bursts of star formation.
Until now, however, astronomers have been unable to directly observe these powerful outflows in the very early universe, where such mechanisms are essential to prevent galaxies from growing too big, too fast.
Spilker’s observations with the Atacama Large Millimeter/submillimeter Array (ALMA), show — for the first time — a powerful galactic wind of molecules in a galaxy seen when the universe was only 1 billion years old. This result provides insights into how certain galaxies in the early universe were able to self-regulate their growth so they could continue forming stars across cosmic time.
Astronomers have observed winds with the same size, speed and mass in nearby starbursting galaxies, but the new ALMA observation is the most distant unambiguous outflow ever seen in the early universe.
The ALMA image (circle call out) shows the location of hydroxyl (OH) molecules. These molecules trace the location of star-forming gas as it is fleeing the galaxy, driven by either supernovas or a black-hole powered “wind.” The background star field (Blanco Telescope Dark Energy Survey) shows the location of the galaxy. The circular, double-lobe shape of the distant galaxy is due to the distortion caused by the cosmic magnifying effect of an intervening galaxy.
The galaxy, known as SPT2319-55, is more than 12 billion light-years away. It was discovered by the National Science Foundation’s South Pole Telescope.
ALMA was able to observe this object at such tremendous distance with the aid of a gravitational lens provided by a different galaxy that sits almost exactly along the line of sight between Earth and SPT2319-55. Gravitational lensing — the bending of light due to gravity — magnifies the background galaxy to make it appear brighter, which allows the astronomers to observe it in more detail than they would otherwise be able to. Astronomers use specialized computer programs to unscramble the effects of gravitational lensing to reconstruct an accurate image of the more-distant object.
This lens-aided view revealed a powerful wind of star-forming gas exiting the galaxy at nearly 800 kilometers per second. Rather than a constant, gentle breeze, the wind is hurtling away in discrete clumps, removing the star-forming gas just as quickly as the galaxy can turn that gas into new stars.
The outflow was detected by the millimeter-wavelength signature of a molecule called hydroxyl (OH), which appeared as an absorption line: essentially, the shadow of an OH fingerprint in the galaxy’s bright infrared light.
Molecular winds are an efficient way for galaxies to self-regulate their growth, the researchers note. These winds are probably triggered by either the combined effects of all the supernova explosions that go along with rapid, massive star formation, or by a powerful release of energy as some of the gas in the galaxy falls down onto the supermassive black hole at its center.
“So far, we have only observed one galaxy at such a remarkable cosmic distance, but we’d like to know if winds like these are also present in other galaxies to see just how common they are,” Spilker concluded. “If they occur in basically every galaxy, we know that molecular winds are both ubiquitous and also a really common way for galaxies to self-regulate their growth.”
The NASA Hubble Space Telescope image of the Antennae galaxies at the top of the page is the sharpest yet of this merging pair of galaxies. During the course of the collision, billions of stars will be formed. The brightest and most compact of these star birth regions are called super star clusters.
The two spiral galaxies started to interact a few hundred million years ago, making the Antennae galaxies one of the nearest and youngest examples of a pair of colliding galaxies. Nearly half of the faint objects in the Antennae image are young clusters containing tens of thousands of stars. The orange blobs to the left and right of image center are the two cores of the original galaxies and consist mainly of old stars criss-crossed by filaments of dust, which appears brown in the image. The two galaxies are dotted with brilliant blue star-forming regions surrounded by glowing hydrogen gas, appearing in the image in pink.
The new image allows astronomers to better distinguish between the stars and super star clusters created in the collision of two spiral galaxies. By age dating the clusters in the image, astronomers find that only about 10 percent of the newly formed super star clusters in the Antennae will survive beyond the first 10 million years. The vast majority of the super star clusters formed during this interaction will disperse, with the individual stars becoming part of the smooth background of the galaxy. It is however believed that about a hundred of the most massive clusters will survive to form regular globular clusters, similar to the globular clusters found in our own Milky Way galaxy.
The Antennae galaxies take their name from the long antenna-like “arms” extending far out from the nuclei of the two galaxies, best seen by ground-based telescopes. These “tidal tails” were formed during the initial encounter of the galaxies some 200 to 300 million years ago. They give us a preview of what may happen when our Milky Way galaxy will collide with the neighboring Andromeda
The Daily Galaxy via University of Texas and NRAO
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