The galaxy M32 is a small
satellite of the larger, spiral Andromeda Galaxy (M31), as shown in this
visible-light image. The inset is a combined radio/optical/X-ray image
of M32. The diffuse purple is the visible starlight of M32. The central
white object in the inset is the center of M32, where there is both
radio and X-ray emission. Red shows radio-emitting objects, including a
pair of presumed planetary nebulae (left center), and the green is an
object strongly emitting X-rays.
Credit: Bill Saxton, NRAO/AUI/NSF; Yang et al.; NASA, ESA, Digitized Sky Survey 2 (Acknowledgement: Davide DeMartin).
Thanks to the extraordinary sensitivity
of the Karl G. Jansky Very Large Array (VLA), astronomers have detected
what they believe is the long-sought radio emission coming from a
supermassive black hole at the center of one of our closest neighboring
galaxies. Evidence for the black hole's existence previously came only
from studies of stellar motions in the galaxy and from X-ray
observations.
The galaxy, called Messier 32 (M32), is a satellite of the Andromeda
Galaxy, our own Milky Way's giant neighbor. Unlike the Milky Way and
Andromeda, which are star-forming spiral galaxies, M32 is an elliptical
galaxy, with little star formation. About 2.5 million light-years from
Earth, M32 is much smaller than either the Milky Way or Andromeda.
Supermassive black holes are found at the cores of most galaxies, and
as those black holes draw in matter from their surroundings, jets of
material propelled to speeds close to that of light by the black holes
often generate radio waves detectable with radio telescopes. The
intensity of this radio emission depends on how voraciously the black
hole is consuming surrounding matter. The central black holes of the
Milky Way and Andromeda are quite weak radio emitters compared to many
other galaxies.
'The very faint radio emission we think is coming from M32's central
black hole indicates that this object's activity is among the weakest
yet found, along with the Milky Way and Andromeda,' said Yang Yang, of
Nanjing University in China. 'Studying such quiescent black holes gives
us an excellent opportunity to advance our presently-poor understanding
of their physics,' she added.
The discovery was made possible by the dramatic improvement in
sensitivity, or the ability to detect extremely faint radio waves,
produced by a decade-long, $98 million upgrade of the VLA's electronic
systems that was completed in 2012. The new VLA observations were able
to detect radio emission roughly 90 times fainter than previous studies
of M32.
The VLA image showed a faint radio-emitting object at the location
where X-rays are being emitted and around which stars near the galaxy's
center appear to be orbiting. 'This tells us that the radio emission
most likely is coming from the black hole, but we want to do further
observations to confirm this,' Yang said.
M32's black hole contains about 2.5 million times the mass of the Sun, compared to the Milky Way black hole's four million.
The VLA also revealed three radio-emitting objects that, the
scientists said, are planetary nebulae previously seen with
visible-light telescopes. Planetary nebulae are spheres of gas blown off
during late stages in the lives of stars like our Sun. The M32 VLA
image represents the first detection by a radio telescope of such
objects at the far edges of our Local Group of galaxies.
Yang led a research team of astronomers from China and the U.S.
Lorant Sjouwerman of the National Radio Astronomy Observatory was
instrumental in obtaining and reducing the VLA data for the study. The
scientists are reporting their findings in the Astrophysical Journal Letters.
The National Radio Astronomy Observatory is a facility of the
National Science Foundation, operated under cooperative agreement by
Associated Universities, Inc.
Story Source:
The above post is reprinted from
materials provided by
National Radio Astronomy Observatory.
Note: Materials may be edited for content and length.
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