A massive cluster of galaxies, called SpARCS1049+56, can be seen in this two-panel, multi-wavelength view from NASA's Hubble and Spitzer space telescopes. At the middle of the picture is the largest, central member of the family of galaxies (upper right red dot of central pair). Unlike other central galaxies in clusters, this one is bursting with the birth of new stars.
Scientists say this star birth was triggered by a collision between a smaller galaxy and the giant, central galaxy. The smaller galaxy's wispy, shredded parts, called a tidal tail, can be seen coming out below the larger galaxy. Throughout this region are features called "beads on a string," which are areas where gas has clumped to form new stars.
This type of "feeding" mechanism for galaxy clusters — where gas from the merging of galaxies is converted to new stars — is rare.
The Hubble data in this image show infrared light with a wavelength of 1 micron in blue and 1.6 microns in green. The Spitzer data show infrared light of 3.6 microns in red.
Astronomers have discovered a rare beast of a galaxy cluster whose heart is bursting with new stars. The unexpected find, made with the help of NASA's Spitzer and Hubble space telescopes, suggests that behemoth galaxies at the cores of these massive clusters can grow significantly by feeding off gas stolen from other galaxies.
"Usually, the stars at the centers of galaxy clusters are old and
dead, essentially fossils," said Tracy Webb of McGill University,
Montreal, Canada, lead author of a new paper on the findings published
in the Aug. 20 issue of The Astrophysical Journal. "But we think the
giant galaxy at the center of this cluster is furiously making new
stars after merging with a smaller galaxy."
Galaxy clusters are vast families of galaxies bound and grouped by
the ties of gravity. Our own Milky Way resides in a small galaxy group,
called the Local Group, which itself is on the periphery of the vast
Laniakea supercluster of 100,000 galaxies. (Laniakea is Hawaiian for
"immeasurable heaven.")
The cluster in the new study, referred to by astronomers as
SpARCS1049+56, has at least 27 galaxy members, and a combined mass
equal to nearly 400 trillion suns. It is located 9.8 billion
light-years away in the Ursa Major constellation. The object was
initially discovered using Spitzer and the Canada-France-Hawaii
Telescope, located on Mauna Kea in Hawaii, and confirmed using the W.M.
Keck Observatory, also on Mauna Kea.
What makes this cluster unique is its luminous heart of new stars. At
the core of most massive galaxy clusters lies one hulking galaxy that
usually doesn't produce new stars very quickly. The galaxy dominating
the cluster SpARCS1049+56 is rapidly spitting out an enormous number of
stars — about 860 new ones a year. For reference, our Milky Way makes
only about one to two stars per year.
"With Spitzer's infrared camera, we can actually see the ferocious
heat from all these hot young stars," said co-author Jason Surace from
NASA's Spitzer Science Center at the California Institute of Technology
in Pasadena, California. Spitzer detects infrared light, so it can see
the warm glow of hidden, dusty regions where stars form.
Follow-up studies with Hubble in visible light helped confirm the
source of the fuel, or gas, for the new stars.
A smaller galaxy seems
to have recently merged with the monster galaxy in the middle of the
cluster, lending its gas to the larger galaxy and igniting a fury of
new stars.
"Hubble found a train wreck of a merger at the center of this galaxy," said Webb.
Hubble specifically detected features in the smaller, merging galaxy
called "beads on a string," which are pockets of gas that condense
where new stars are forming. Beads on a string are telltale signs of
collisions between gas-rich galaxies, a phenomenon known to astronomers
as wet mergers, where "wet" refers to the presence of gas. In these
smash-ups, the gas is quickly converted to new stars.
Dry mergers, by contrast, occur when galaxies with little gas collide
and no new stars are formed. Typically, galaxies at the centers of
clusters grow in mass through dry mergers at their core, or by
siphoning gas into their centers.
The new discovery is one of the first known cases of a wet merger at
the core of a distant galaxy cluster. Hubble previously discovered
another, closer galaxy cluster containing a wet merger, but it wasn't
forming stars as vigorously.
The researchers are planning more studies to find out how common
galaxy clusters like SpARCS1049+56 are. The cluster may be an outlier —
or it may represent an early time in our universe when gobbling up
gas-rich galaxies was the norm.
Contact
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
whitney.clavin@jpl.nasa.gov
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Contact
Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California
818-354-4673
whitney.clavin@jpl.nasa.gov
Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4514
villard@stsci.edu
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Source: HubbleSite
