Hubble Witnesses Spectacular Flaring in Extragalactic
Jet from M87's Black Hole
Tuesday, April 14, 2009
A flare-up in a jet of matter blasting from a monster black hole is
giving astronomers an incredible light show.
The outburst is coming from a blob of matter, called HST-1,
embedded in the jet, a powerful narrow beam of hot gas produced by
a supermassive black hole residing in the core of the giant
elliptical galaxy M87. HST-1 is so bright that it is outshining
even M87's brilliant core, whose monster black hole is one of the
most massive yet discovered.
The glowing gas clump has taken astronomers on a rollercoaster ride
of suspense. Astronomers watched HST-1 brighten steadily for
several years, then fade, and then brighten again. They say it's
hard to predict what will happen next.
NASA's Hubble Space Telescope has been following the surprising
activity for seven years, providing the most detailed
ultraviolet-light view of the event. Other telescopes have been
monitoring HST-1 in other wavelengths, including radio and X-rays.
The Chandra X-ray Observatory was the first to report the
brightening in 2000. HST-1 was first discovered and named by Hubble
astronomers in 1999. The gas knot is 214 light-years from the
galaxy's core.
The flare-up may provide insights into the variability of black
hole jets in distant galaxies, which are difficult to study because
they are too far away. M87 is located 54 million light-years away
in the Virgo Cluster, a region of the nearby universe with the
highest density of galaxies.
"I did not expect the jet in M87 or any other jet powered by
accretion onto a black hole to increase in brightness in the way
that this jet does," says astronomer Juan Madrid of McMaster
University in Hamilton, Ontario, who conducted the Hubble study.
"It grew 90 times brighter than normal. But the question is, does
this happen to every single jet or active nucleus, or are we seeing
some odd behavior from M87?"
Hubble gives astronomers a unique near-ultraviolet view of the
flare that cannot be accomplished with ground-based telescopes.
"Hubble's sharp vision allows it to resolve HST-1 and separate it
from the black hole," Madrid explains.
Despite the many observations by Hubble and other telescopes,
astronomers are not sure what is causing the brightening. One of
the simplest explanations is that the jet is hitting a dust lane or
gas cloud and then glows due to the collision. Another possibility
is that the jet's magnetic field lines are squeezed together,
unleashing a large amount of energy. This phenomenon is similar to
how solar flares develop on the Sun and is even a mechanism for
creating Earth's auroras.
The disk around a rapidly spinning black hole has magnetic field
lines that entrap ionized gas falling toward the black hole. These
particles, along with radiation, flow rapidly away from the black
hole along the magnetic field lines. The rotational energy of the
spinning accretion disk adds momentum to the outflowing jet.
Madrid assembled seven years' worth of Hubble archival images of
the jet to capture changes in the HST-1's behavior over time.
Hubble's view of the event. Some of the images came from observing
programs that studied the galaxy, but not the jet.
He found data from the Space Telescope Imaging Spectrograph (STIS)
that showed a noticeable brightening between 1999 and 2001. In
images from 2002 to 2005, HST-1 continued to rise steadily in
brightness. In 2003 the jet knot was more brilliant than M87's
luminous core. In May 2005 HST-1 became 90 times brighter than it
was in 1999. After May 2005 the flare began to fade, but it
intensified again in November 2006. This second outburst was
fainter than the first one.
"By watching the outburst over several years, I was able to follow
the brightness and see the evolution of the flare over time,"
Madrid says. "We are lucky to have telescopes like Hubble and
Chandra, because without them we would see the increase in
brightness in the core of M87, but we would not know where it was
coming from."
Madrid hopes that future observations of HST-1 will reveal the
cause of the mysterious activity. "We hope the observations will
yield some theories that will give us some good explanations as to
the mechanism that is causing the flaring," Madrid says.
"Astronomers would like to know if this is an intrinsic instability
of the jet when it plows its way out of the galaxy, or if it is
something else."
The study's results are published in the April 2009 issue of The
Astronomical Journal.
For images and more information, visit:
http://hubblesite.org/news/2009/16
The Hubble Space Telescope is a project of international
cooperation between NASA and the European Space Agency (ESA) and is
managed by NASA's Goddard Space Flight Center (GSFC) in Greenbelt,
Md. The Space Telescope Science Institute (STScI) conducts Hubble
science operations. The institute is operated for NASA by the
Association of Universities for Research in Astronomy, Inc.,
Washington, D.C. STScI is an International Year of Astronomy 2009
(IYA 2009) program partner.
###
Source: Space Telescope Science Institute (STScI)
Thanks to NewsWise for this
article.