ASASSN-14li
Credit Spectrum: NASA/CXC/U.Michigan/J.Miller et al.;
Illustration: NASA/CXC/M.Weiss
Astronomers have observed material being blown away from a black hole after it tore a star apart, as reported in our press release. This event, known as a "tidal disruption," is depicted in the artist's illustration.
Astronomers used a trio of X-ray telescopes - NASA's Chandra X-ray Observatory, Swift Gamma Ray Burst Explorer, and ESA's XMM-Newton - to observe a tidal disruption located in the center of a galaxy about 290 million light years
away. This makes this tidal disruption, dubbed ASASSN-14li, the closest
tidal disruption discovered in ten years. The event was discovered in
an optical search by the All-Sky Automated Survey for Supernovae
(ASAS-SN) in November 2014. Theory predicts that early in the evolution
of a tidal disruption, material from the shredded star (seen as the
reddish-orange streak) should be pulled towards the black hole at a high
rate, generating a huge amount of light.
The amount of light should decline as the disrupted material falls onto
the black hole, shown as the small black circle in the upper left of
the illustration. In the case of ASASSN-14li, astronomers estimate the
mass of the black hole is a few million times that of the Sun.
Gas often falls toward black holes by spiraling inward in a disk. But
how this process starts has remained a mystery. In ASASSN-14li,
astronomers were able to witness the formation of such a disk by looking
at the X-ray light at different wavelengths
(known as the "X-ray spectrum") and tracking how that changed over
time. The researchers determined that the observed X-rays come from
material that is either very close to or is actually in the smallest
possible stable orbit around the black hole.
The illustration shows a disk of stellar debris around the black hole
in the upper left of the illustration, and a long tail of debris that
has been flung away from the black hole.
The X-ray spectrum obtained with Chandra (seen in the inset box) and
XMM-Newton both show clear evidence for absorption lines, i.e. dips in
X-ray intensity over a narrow range of wavelengths. In an X-ray light
version of the Doppler Shift, the absorption lines are shifted to bluer
wavelengths than expected, giving evidence for a wind blowing towards us
and away from the black hole.
The presence of a wind moving away from the black hole is shown as
the bluish white lines in the artist's illustration. The wind is not
moving fast enough to escape the black hole's gravitational grasp. An
alternative explanation for the relatively low speed is that gas from
the disrupted star is following an elliptical orbit around the black
hole and is observed at the greatest distance from the black hole where
it is traveling the slowest. These results confirm recent theoretical
predictions for the structure and evolution of tidal disruptions events.
These results appeared in a paper in the October 22nd issue of the
journal Nature. The authors of that paper are Jon M. Miller (University
of Michigan), Jelle Kastra (SRON Institute for Space Research), Cole
Miller (University of Maryland, College Park), Mark Reynolds (Michigan),
Gregory Brown (University of Warwick), Bradley Cenko (Maryland), Jeremy
Drake (Harvard-Smithsonian Center for Astrophysics), Suvi Gezari
(Maryland), James Guillochon (CfA), Kayhan Gultekin (Michigan), Jimmy
Irwin (University of Alabama), Andrew Levan (Warwick), Dipankar Maitra
(Wheaton College), Peter Maksym (Alabama), Richard Mushotsky (Maryland),
Paul O'Brien (University of Leicester), Fritz Paerels (Columbia
University), Jelle de Plaa (SRON), Enrico Ramirez-Ruiz (University of
California, Santa Cruz), Tod Strohmayer (Maryland), and Nial Tanvir
(Leicester).
NASA's Marshall Space Flight Center in Huntsville, Alabama, manages
the Chandra program for NASA's Science Mission Directorate in
Washington. The Smithsonian Astrophysical Observatory in Cambridge,
Massachusetts, controls Chandra's science and flight operations. Swift
is managed by NASA's Goddard Space Flight Center in Greenbelt, Maryland.
Fast Facts for ASASSN-14li:
Category: Black Holes
Coordinates (J2000): RA 12h 48m 15.20s | Dec +17° 46' 26.20"
Constellation: Coma Berenices
Observation Date: 08 and 11 Dec 2014
Observation Time: 22 hours.
Obs. ID: 17566, 17567
Instrument: HRC
References: Miller, J. et al, 2015, Nature (accepted)
Distance Estimate: About 290 million light years (z=0.0206)
Source: NASA’s Chandra X-ray Observatory
