This 3-D spectro-imaging data cube was produced using software called
OsrsVol, short for OSIRIS-Volume Display. W. M. Keck Observatory Science
Operations Lead Randy Campbell developed this custom volume rendering
tool to separate G3, G4, and G5 from the background emission. Once the
3-D analysis was performed, the team could clearly distinguish the
G-objects, which allowed them to follow their movement and see how they
behave around the supermassive black hole.
Maunakea, Hawaii – Astronomers have discovered
several bizarre objects at the Galactic Center that are concealing their true
identity behind a smoke screen of dust; they look like gas clouds, but behave like
stars.
At
today’s American Astronomical Society Meeting in Denver, a team of researchers
led by UCLA Postdoctoral Scholar Anna Ciurlo announced their results, which
they obtained using 12 years of data taken from W. M. Keck Observatory on
Maunakea, Hawaii.
“These
compact dusty stellar objects move extremely fast and close to our Galaxy’s
supermassive black hole. It is fascinating to watch them move from year to
year,” said Ciurlo. “How did they get there? And what will they become? They
must have an interesting story to tell.”
The
researchers made their discovery by obtaining spectroscopic measurements of the
Galactic Center’s gas dynamics using Keck Observatory’s OH-Suppressing Infrared
Imaging Spectrograph (OSIRIS).
“We
started this project thinking that if we looked carefully at the complicated
structure of gas and dust near the supermassive black hole, we might detect
some subtle changes to the shape and velocity,” said Randy Campbell, science
operations lead at Keck Observatory. “It was quite surprising to detect several
objects that have very distinct movement and characteristics that place them in
the G-object class, or dusty stellar objects.”
Astronomers
first discovered G-objects at the Milky Way’s monster black hole more than a
decade ago; G1 was first seen in 2004, and G2 was discovered in 2012. Both were
thought to be gas clouds until they made their closest approach to the
supermassive black hole. G1 and G2 somehow managed to survive the black hole’s
gravitational pull, which can shred gas clouds apart.
“If
they were gas clouds, G1 and G2 would not have been able to stay intact,” said
UCLA Astronomy Professor Mark Morris, a co-principal investigator and fellow
member of UCLA’s Galactic Center Orbits Initiative (GCOI). “Our view of the G-objects
is that they are bloated stars – stars that have become so large that the tidal
forces exerted by the central black hole can pull matter off of their stellar
atmospheres when the stars get close enough, but have a stellar core with
enough mass to remain intact. The question is then, why are they so large?”
It appears that a lot of
energy was dumped into the G-objects, causing them to swell up and grow larger
than typical stars.
GCOI thinks that these
G-objects are the result of stellar mergers - where two stars orbiting each
other, known as binaries, crash into each other due to the gravitational
influence of the giant black hole. Over a long period of time, the black hole’s
gravity alters the binary stars’ orbits until the duo collides. The combined
object that results from this violent merger could explain where the excess
energy came from.
“In
the aftermath of such a merger, the resulting single object would be
"puffed up”, or distended, for a rather long period of time, perhaps a
million years, before it settles down and appears like a normal-sized star,”
said Morris.
“This is what I find most exciting,” said Andrea Ghez, founder and
director of GCOI. “If these objects are indeed binary star systems that have
been driven to merge through their interaction with the central supermassive
black hole, this may provide us with insight into a process which may be
responsible for the recently discovered stellar mass black hole mergers that
have been detected through gravitational waves.”
What
makes G-objects unusual is their “puffiness.” It is rare for a star to be
cloaked by a layer of dust and gas so thick that astronomers do not see the
star directly. They only see the glowing envelope of dust. To see the objects through
their hazy environment, Campbell developed a tool called OSIRIS-Volume Display
(OsrsVol).
“OsrsVol allowed us to
isolate these G-objects from the background emission and analyze the spectral
data in three dimensions: two spatial
dimensions, and the wavelength dimension that provides velocity information,” said Campbell. “Once we were able to distinguish
the objects in a 3-D data cube, we could then track their motion over time
relative to the black hole.”
“Keck
Observatory has been observing the Galactic Center every year for 20 years with
some of the best instruments and technologies,” said Ciurlo. “This alone gives
a very high quality and consistent data set, which allowed us to go deep into
the analysis of the data.
These newly discovered infrared
sources could potentially be G-objects - G3, G4, and G5 – because they share
the physical characteristics of G1 and G2.
The team will continue to follow the size and shape of the G-objects’
orbits, which could provide important clues as to how they formed.
The astronomers will especially be paying close attention when these
dusty stellar compact objects make their closest approach to the supermassive
black hole. This will allow them to further observe their behavior and see whether
the objects remain intact just as G1 and G2 did, or become a snack for the
supermassive black hole. Only then will they give away their true nature.
“We’ll have to wait a few decades for this to happen; about 20 years for
G3, and decades longer for G4 and G5,” said Morris. “In the meantime, we can
learn more about these puffballs by following their dynamical evolution using
OSIRIS.”
“Understanding G-objects can teach us a lot about the Galactic Center’s
fascinating and still mysterious environment. There are so many things going on
that every localized process can help explain how this extreme, exotic
environment works,” said Ciurlo.
Source: W.M. Keck Observatory
This research is conducted through a collaboration
between Randy Campbell at the W.M. Keck
Observatory, members of the Galactic
Center Group at UCLA (Anna Ciurlo, Mark Morris, and Andrea Ghez) and Rainer Schoedel of
the Instituto de Astrofisica de Andalucia (CSIC) in Granada, Spain.
About OSIRIS
The OH-Suppressing Infrared Imaging
Spectrograph (OSIRIS) is one of W. M. Keck Observatory’s "integral field
spectrographs." The instrument works behind the adaptive optics system,
and uses an array of lenslets to sample a small rectangular patch of the sky at
resolutions approaching the diffraction limit of the 10-meter Keck Telescope.
OSIRIS records an infrared spectrum at each point within the patch in a single
exposure, greatly enhancing its efficiency and precision when observing small
objects such as distant galaxies. It is used to characterize the dynamics and
composition of early stages of galaxy formation. Support for this technology
was generously provided by the Heising-Simons Foundation and the National
Science Foundation.
About the Galactic Center Orbits Initiative
The Galactic Center Orbits Initiative (GCOI), founded and directed by Andrea Ghez in 1994, is dedicated to studying the innermost regions of the Milky Way at the highest angular resolution possible in order to understand the formation and evolution of galaxies and their central supermassive black holes through the measurement of orbital motion. At the heart of GCOI today is a data set that has been collected over 23 years at the W. M. Keck Observatory. This data set led to the discovery of the supermassive black hole at the center of our Galaxy as well as an unexpected nearby stellar population; it holds the promise of testing Einstein’s General Theory of Relativity near a supermassive hole, a new and unexplored regime for this fundamental force of nature. This rich data set has enabled studies of a host of other topics including black hole accretion, extreme star formation, and nuclear star cluster evolution. GCOI’s core collaboration includes over 30 people from UCLA, UCB, Caltech, Keck Observatory, and IAA-CSIC, with funding provided by the National Science Foundation, the W. M. Keck Foundation, the Heising-Simons Foundation, and the Gordon & Betty Moore Foundation. For more information, visit www.galacticcenter.astro.ucla.edu.
About W.M. Keck Observatory
The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. The data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
About the Galactic Center Orbits Initiative
The Galactic Center Orbits Initiative (GCOI), founded and directed by Andrea Ghez in 1994, is dedicated to studying the innermost regions of the Milky Way at the highest angular resolution possible in order to understand the formation and evolution of galaxies and their central supermassive black holes through the measurement of orbital motion. At the heart of GCOI today is a data set that has been collected over 23 years at the W. M. Keck Observatory. This data set led to the discovery of the supermassive black hole at the center of our Galaxy as well as an unexpected nearby stellar population; it holds the promise of testing Einstein’s General Theory of Relativity near a supermassive hole, a new and unexplored regime for this fundamental force of nature. This rich data set has enabled studies of a host of other topics including black hole accretion, extreme star formation, and nuclear star cluster evolution. GCOI’s core collaboration includes over 30 people from UCLA, UCB, Caltech, Keck Observatory, and IAA-CSIC, with funding provided by the National Science Foundation, the W. M. Keck Foundation, the Heising-Simons Foundation, and the Gordon & Betty Moore Foundation. For more information, visit www.galacticcenter.astro.ucla.edu.
About W.M. Keck Observatory
The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two, 10-meter optical/infrared telescopes on the summit of Maunakea on the Island of Hawaii feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. The data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.
