Such encounters between dwarf galaxies are normally seen billions of light-years away and therefore occurred billions of years ago. But these galaxies, members of Hickson Compact Group 31, are relatively nearby, only 166 million light-years away.
New images of this foursome by NASA's Hubble Space Telescope offer a window into the universe's formative years when the buildup of large galaxies from smaller building blocks was common.
Astronomers have known for decades that these dwarf galaxies are gravitationally tugging on each other. Their classical spiral shapes have been stretched like taffy, pulling out long streamers of gas and dust. The brightest object in the Hubble image is actually two colliding galaxies. The entire system is aglow with a firestorm of star birth, triggered when hydrogen gas is compressed by the close encounters between the galaxies, and collapses to form stars.
The Hubble observations have added important clues to the story of this interacting group, allowing astronomers to determine when the encounter began and to predict a future merger.
"We found the oldest stars in a few ancient globular star clusters that date back to about 10 billion years ago. Therefore, we know the system has been around for a while," says astronomer Sarah Gallagher of The University of Western Ontario in London, Ontario, leader of the Hubble study. "Most other dwarf galaxies like these interacted billions of years ago, but these galaxies are just coming together for the first time. This encounter has been going on for at most a few hundred million years, the blink of an eye in cosmic history. It is an extremely rare local example of what we think was a quite common event in the distant universe."
Everywhere the astronomers looked in this group they found batches of infant star clusters and regions brimming with star birth. The entire system is rich in hydrogen gas, the stuff of which stars are made. Gallagher and her team used Hubble's Advanced Camera for Surveys to resolve the youngest and brightest of those clusters, which allowed them to calculate the clusters' ages, trace the star-formation history, and determine that the galaxies are undergoing the final stages of galaxy assembly.
The analysis was bolstered by infrared data from NASA's Spitzer Space Telescope and ultraviolet observations from the Galaxy Evolution Explorer (GALEX) and NASA's Swift satellite. Those data helped the astronomers measure the total amount of star formation in the system. "Hubble has the sharpness to resolve individual star clusters, which allowed us to age-date the clusters," Gallagher adds.
Hubble reveals that the brightest clusters, hefty groups each holding at least 100,000 stars, are less than 10 million years old. The stars are feeding off of plenty of gas. A measurement of the gas content shows that very little has been used up -- further proof that the "galactic fireworks" seen in the images are a recent event. The group has about five times as much hydrogen gas as our Milky Way Galaxy.
"This is a clear example of a group of galaxies on their way toward a merger because there is so much gas that is going to mix everything up," Gallagher says. "The galaxies are relatively small, comparable in size to the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Their velocities, measured from previous studies, show that they are moving very slowly relative to each other, just 134,000 miles an hour (60 kilometers a second). So it's hard to imagine how this system wouldn't wind up as a single elliptical galaxy in another billion years."
Adds team member Pat Durrell of Youngstown State University: "The four small galaxies are extremely close together, within 75,000 light-years of each other -- we could fit them all within our Milky Way."
Why did the galaxies wait so long to interact? Perhaps, says Gallagher, because the system resides in a lower-density region of the universe, the equivalent of a rural village. Getting together took billions of years longer than it did for galaxies in denser areas.
Hickson Compact Group 31 is one of 100 compact galaxy groups catalogued by Canadian astronomer Paul Hickson.
Gallagher's results appear in the February issue of The Astronomical Journal.
Her science team consists of Pat Durrell (Youngstown State University), Debra Elmegreen (Vassar College), Rupali Chandar (University of Toledo), Jayanne English (University of Manitoba), Jane Charlton, Caryl Gronwal, and Jason Young (Penn State), Panayiotis Tzanavaris (NASA's Goddard Space Flight Center), Kelsey Johnson (University of Virginia), Claudia Mendes de Oliveira (University of Sao Paulo), Brad Whitmore (STScI), Ann Hornschemeier (NASA's Goddard Space Flight Center), Aparna Maybhate (STScI), and Ann Zabludoff (University of Arizona).
For images and more information about Hickson Compact Group 31, visit:http://hubblesite.org/news/2010/08
Donna Weaver | Newswise Science News
New NASA study improves search for habitable worlds
20.10.2017 | NASA/Goddard Space Flight Center
Physics boosts artificial intelligence methods
19.10.2017 | California Institute of Technology
University of Maryland researchers contribute to historic detection of gravitational waves and light created by event
On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...
Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.
Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....
Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).
When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...
Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.
How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...
Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.
It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...
17.10.2017 | Event News
10.10.2017 | Event News
10.10.2017 | Event News
20.10.2017 | Information Technology
20.10.2017 | Materials Sciences
20.10.2017 | Interdisciplinary Research