The
orbit of S0-2 (light blue) located near the Milky Way's supermassive
black hole will be used to test Einstein's Theory of General Relativity
and generate potentially new gravitational models.
The UCLA Galactic Center Group takes a photo together during a visit to
Keck Observatory, located atop Maunakea, Hawaii. Members of the group
will return to the Observatory this spring to begin observations of S0-2
as the star travels towards its closest distance to the Galactic
Center's supermassive black hole.
No companion found for famous young bright star orbiting Milky Way’s supermassive black
hole
Maunakea, Hawaii – Astronomers have the “all-clear” for an exciting test of Einstein’s Theory of General Relativity, thanks to a new discovery about S0-2’s star status. Credit: S. Sakai/A.GHEZ/W.M. Keck Observatory,/ UCLA Galactic Center Group
Up until now, it was thought that S0-2
may be a binary, a system where two stars circle around each other. Having such
a partner would have complicated the upcoming gravity test.
But in a study published recently in The Astrophysical Journal, a team of astronomers led by a UCLA scientist from Hawaii
has found that S0-2 does not have a significant other after all, or at least
one that is massive enough to get in the way of critical measurements that
astronomers need to test Einstein’s theory.
The researchers made their discovery by
obtaining spectroscopic measurements of S0-2 using W. M. Keck Observatory’s
OH-Suppressing Infrared Imaging Spectrograph (OSIRIS) and Laser Guide Star
Adaptive Optics.
“This is the first study to investigate
S0-2 as a spectroscopic binary,” said lead author Devin Chu of Hilo, an
astronomy graduate student with UCLA’s Galactic Center Group. “It’s incredibly
rewarding. This study gives us confidence that a S0-2 binary system will not
significantly affect our ability to measure gravitational redshift.”
Einstein’s Theory of
General Relativity predicts that light coming from a strong gravitational field
gets stretched out, or “redshifted.” Researchers expect to directly measure
this phenomenon beginning in the spring as S0-2 makes its closest approach to the
supermassive black hole at the center of our Milky Way galaxy.
This
will allow the Galactic Center Group to witness the star being pulled at
maximum gravitational strength – a point where any deviation to Einstein’s
theory is expected to be the greatest.
“It
will be the first measurement of its kind,” said co-author Tuan Do, deputy
director of the Galactic Center Group. “Gravity is the least well-tested of the
forces of nature. Einstein’s theory has passed all other tests with flying
colors so far, so if there are deviations measured, it would certainly raise
lots of questions about the nature of gravity!”
“We have
been waiting 16 years for this,” said Chu. “We are anxious to see how the star
will behave under the black hole’s violent pull. Will S0-2 follow Einstein’s
theory or will the star defy our current laws of physics? We will soon find
out!”
The study
also sheds more light on the strange birth of S0-2 and its stellar neighbors in
the S-Star Cluster. The fact that these stars exist so close to the
supermassive black hole is unusual because they are so young; how they could’ve
formed in such a hostile environment is a mystery.
“Star
formation at the Galactic Center is difficult because the brute strength of
tidal forces from the black hole can tear gas clouds apart before they can
collapse and form stars,” said Do.
“S0-2 is a
very special and puzzling star,” said Chu. “We don’t typically see young, hot stars
like S0-2 form so close to a supermassive black hole. This means that S0-2 must
have formed a different way.”
There
are several theories that provide a possible explanation, with S0-2 being a
binary as one of them. “We were able to put an upper limit on the mass
of a companion star for S0-2,” said Chu. This
new constraint brings astronomers closer to understanding this unusual object.
“Stars
as massive as S0-2 almost always have a binary companion. We are lucky that
having no companion makes the measurements of general relativistic effects
easier, but it also deepens the mystery of this star,” said Do.
The
Galactic Center Group now plans to study other S-Stars orbiting the
supermassive black hole, in hopes of differentiating between the varying theories
that attempt to explain why S0-2 is single.
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 Adaptive Optics
W. M. Keck Observatory is a distinguished leader in the field of
adaptive optics (AO), a breakthrough technology that removes the distortions
caused by the turbulence in the Earth’s atmosphere. Keck Observatory
pioneered the astronomical use of both natural guide star (NGS) and laser guide
star adaptive optics (LGS AO) and current systems now deliver images three to
four times sharper than the Hubble Space Telescope. AO has imaged the four
massive planets orbiting the star HR8799, measured the mass of the giant black
hole at the center of our Milky Way Galaxy, discovered new supernovae in
distant galaxies, and identified the specific stars that were their
progenitors. Support for
this technology was generously provided by the Gordon and Betty Moore
Foundation, W. M. Keck Foundation, the National Science Foundation, and other
Friends of Keck including The Bob and Renee Parsons Foundation, Change Happens
Foundation, Mt. Cuba Astronomical Foundation, and Sanford and Jeanne Robertson.
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 wish to 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.
Article Summary
A team of astronomers led by Devin Chu, a UCLA scientist from
Hawaii, has found that S0-2 does not have a significant other after all,
or at least
one that is massive enough to get in the way of critical measurements
that
astronomers need to test Einstein’s Theory of General Relativity. Up
until now, it was thought that S0-2 may be a binary, a system where two
stars circle around each other. Having such a partner would have
complicated the upcoming gravity test.
Contact
Mari-Ela Chock,
Communications Officer
(808) 554-0567
mchock@keck.hawaii.edu
Contact
Mari-Ela Chock,
Communications Officer
(808) 554-0567
mchock@keck.hawaii.edu
Source: W.M. Keck Observatory
