The main panel of this graphic contains X-ray data from Chandra (blue) depicting hot gas that was blown away from massive stars near the black hole. Two images of infrared light at different wavelengths from NASA's Hubble Space Telescope show stars (orange) and cool gas (purple). These images are seven light years across at the distance of Sgr A*. A pull-out shows the new EHT image, which is only about 1.8 x 10-5 light years across (0.000018 light years, or about 10 light minutes). (Credit: X-ray: NASA/CXC/SAO; IR: NASA/HST/STScI. Inset: Radio (EHT Collaboration))
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As the Event Horizon Telescope collected
data for its remarkable new image of
the Milky Way's supermassive black hole, a legion of other telescopes including three NASA
X-ray observatories in space was also watching.
Astronomers are using these observations
to learn more about how the black hole in the center of the Milky Way galaxy —
known as Sagittarius A * (Sgr A* for short) — interacts with, and feeds off,
its environment some 27,000 light years from Earth.
When the Event Horizon Telescope (EHT)
observed Sgr A* in April 2017 to make the new image, scientists in the
collaboration also peered at the same black hole with facilities that detect
different wavelengths of light. In this multiwavelength observing campaign,
they assembled X-ray data from NASA's Chandra X-ray Observatory, Nuclear
Spectroscopic Telescope Array (NuSTAR), and the Neil Gehrels Swift Observatory;
radio data from the East Asian Very Long-Baseline Interferometer (VLBI) network
and the Global 3-millimeter VLBI array; and infrared data from the European
Southern Observatory's Very Large Telescope in Chile.
"The Event Horizon Telescope has
captured yet another remarkable image, this time of the giant black hole at the
center of our own home galaxy," said NASA Administrator Bill Nelson.
"Looking more comprehensively at this black hole will help us learn more
about its cosmic effects on its environment, and exemplifies the international
collaboration that will carry us into the future and reveal discoveries we
could never have imagined."
One important goal was to catch X-ray
flares, which are thought to be driven by magnetic processes similar to those
seen on the Sun, but can be tens of millions of times more powerful. These
flares occur approximately daily within the area of sky observed by the EHT, a
region slightly larger than the event horizon of Sgr A*, the point of no return
for matter falling inward. Another goal was to gain a critical glimpse of what
is happening on larger scales. While the EHT result shows striking similarities
between Sgr A* and the previous black hole it imaged, M87*, the wider picture
is much more complex.
"If the new EHT image shows us the
eye of a black hole hurricane, then these multiwavelength observations reveal
winds and rain the equivalent of hundreds or even thousands of miles
beyond," said Daryl Haggard of McGill University in Montreal, Canada, who
is one of the lead scientists of the multiwavelength campaign. "How does
this cosmic storm interact with and even disrupt its galactic
environment?"
One of the biggest ongoing questions
surrounding black holes is exactly how they collect, ingest, or even expel
material orbiting them at near light speed, in a process known as
"accretion." This process is fundamental to the formation and growth
of planets, stars, and black holes of all sizes, throughout the universe.
Chandra images of hot gas around Sgr A*
are crucial for accretion studies because they tell us how much material is
captured from nearby stars by the black hole's gravity, as well as how much
manages to make its way close to the event horizon. This critical information
is not available with current telescopes for any other black hole in the
universe, including M87*.
"Astronomers can largely agree on the
basics — that black holes have material swirling around them and some of it
falls across the event horizon forever," said Sera Markoff of the
University of Amsterdam in the Netherlands, another coordinator of the
multiwavelength observations. "With all of the data that we've gathered
for Sgr A* we can go a lot further than this basic picture."
Scientists in the large international
collaboration compared the data from NASA's high-energy missions and the other
telescopes to state-of-the-art computational models that take into account
factors such as Einstein's general theory of relativity, effects of magnetic
fields, and predictions of how much radiation the material around the black
hole should generate at different wavelengths.
The comparison of the models with the
measurements gives hints that the magnetic field around the black hole is
strong and that the angle between the line of sight to the black hole and its
spin-axis is low — less than about 30 degrees. If confirmed this means that
from our vantage point we are looking down on Sgr A* and its ring more than we
are from side-on, surprisingly similar to EHT's first target M87*.
"None of our models matches the data
perfectly, but now we have more specific information to work from," said
Kazuhiro Hada from the National Astronomical Observatory of Japan. "The
more data we have the more accurate our models, and ultimately our
understanding of black hole accretion, will become."
The researchers also managed to catch
X-ray flares — or outbursts — from Sgr A* during the EHT observations: a faint
one seen with Chandra and Swift, and a moderately bright one seen with Chandra
and NuSTAR. X-ray flares with a similar brightness to the latter are regularly
observed with Chandra, but this is the first time that the EHT simultaneously
observed Sgr A*, offering an extraordinary opportunity to identify the
responsible mechanism using actual images.
The millimeter-wave intensity and
variability observed with EHT increases in the few hours immediately after the
brighter X-ray flare, a phenomenon not seen in millimeter observations a few
days earlier. Analysis and interpretation of the EHT data immediately following
the flare will be reported in future publications.
The EHT team's results are being published
on May 12th in a special issue
of The Astrophysical Journal Letters. The multiwavelength results are mainly described in
papers II and V.
NASA's Marshall Space Flight Center
manages the Chandra program. The Smithsonian Astrophysical Observatory's
Chandra X-ray Center controls science operations from Cambridge, Massachusetts,
and flight operations from Burlington, Massachusetts.
Goddard manages the Swift mission in
collaboration with Penn State, the Los Alamos National Laboratory in New
Mexico, and Northrop Grumman Space Systems in Dulles, Virginia. Other partners
include the University of Leicester and Mullard Space Science Laboratory in the
United Kingdom, Brera Observatory in Italy, and the Italian Space Agency.
NASA's Jet Propulsion Laboratory in Southern California manages NuSTAR for NASA's Science Mission Directorate in Washington. Mission partners and contributors include the Danish Technical University (DTU), the Italian Space Agency (ASI), Columbia University, NASA's Goddard Space Flight Center, Orbital Sciences Corp., the University of California, Berkeley, and NASA's High Energy Astrophysics Science Archive Research Center.
Read more
from NASA's Chandra X-ray Observatory.
For more Chandra images, multimedia and
related materials, visit: http://www.nasa.gov/chandra
Source: NASA
Telescopes Support Studying Milky Way's Black Hole | NASA
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