Galaxy Cluster Abell 2744
Credit: NASA, ESA, M. Montes (IAC), and J. Lotz, M. Mountain, A. Koekemoer, and the HFF Team (STScI).
NASA's Hubble Space Telescope has picked up the faint, ghostly glow of
stars ejected from ancient galaxies that were gravitationally ripped
apart several billion years ago. The mayhem happened 4 billion
light-years away, inside an immense collection of nearly 500 galaxies
nicknamed "Pandora's Cluster," also known as Abell 2744. The scattered
stars are no longer bound to any one galaxy, and drift freely between
galaxies in the cluster.
By observing the light from the orphaned stars, Hubble astronomers
have assembled forensic evidence that suggests as many as six galaxies
were torn to pieces inside the cluster over a stretch of 6 billion
years.
Computer modeling of the gravitational dynamics among galaxies
in a cluster suggest that galaxies as big as our Milky Way are the
likely candidates as the source of the stars. The doomed galaxies would
have been pulled apart like taffy if they plunged through the center of
the galaxy cluster where gravitational tidal forces are strongest.
Astronomers have long hypothesized that the light from scattered stars
should be detectable after such galaxies are disassembled. However, the
predicted "intracluster" glow of stars is very faint and was therefore
a challenge to identify.
"The Hubble data revealing the ghost light are important steps
forward in understanding the evolution of galaxy clusters," said Ignacio
Trujillo of the Instituto de Astrofísica de Canarias (IAC), La Laguna,
Tenerife, Spain, one of the researchers involved in this study of Abell
2744. "It is also amazingly beautiful in that we found the telltale
glow by utilizing Hubble's unique capabilities."
"The results are in good agreement with what has been predicted to
happen inside massive galaxy clusters," added Mireia Montes of the IAC,
lead author of the paper published in the Oct. 1 issue of The
Astrophysical Journal.
The team estimates that the combined light of about 200 billion
outcast stars contributes approximately 10 percent of the cluster's
brightness.
Because these extremely faint stars are brightest at near-infrared
wavelengths of light, the team emphasized that this type of observation
could only be accomplished with Hubble's infrared sensitivity to
extraordinarily dim light.
Hubble measurements determined that the phantom stars are rich in
heavier elements like oxygen, carbon, and nitrogen. This means the
scattered stars must be second- or third-generation stars that were
enriched with the elements forged in the hearts of the universe's
first-generation stars. Spiral galaxies — like the ones believed to be
torn apart — can sustain ongoing star formation that creates chemically
enriched stars.
With the mass of 4 trillion suns, Abell 2744 is a target in the
Frontier Fields program. This ambitious three-year effort teams Hubble
and NASA's other Great Observatories to look at select massive galaxy
clusters to help astronomers probe the remote universe. Galaxy clusters
are so massive that their gravity deflects light passing through them,
magnifying, brightening, and distorting light in a phenomenon called
gravitational lensing. Astronomers exploit this property of space to use
the clusters as a zoom lens to magnify the images of far-more-distant
galaxies that otherwise would be too faint to be seen.
Montes' team used the Hubble data to probe the environment of the
foreground cluster itself. There are five other Frontier Fields
clusters in the program, and the team plans to look for the eerie
"ghost light" in these clusters, too.
CONTACTS
Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
410-338-4514
villard@stsci.edu
Mireia Montes
Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
mireia.montes.quiles@gmail.com
Source: HubbleSite
