Andrew Yee[_1_]
May 16th 07, 05:41 PM
ESA News
http://www.esa.int
16 May 2007
New technique for 'weighing' black holes
ESA's XMM-Newton has helped to find evidence for the existence of
controversial Intermediate Mass Black Holes. Scientists used a new, recently
proven method for determining the mass of black holes.
Nikolai Shaposhnikov and Lev Titarchuk, at NASA's Goddard Space Flight
Center (GSFC), have used the technique to determine the mass of the black
hole, Cygnus X-1, located in the constellation Cygnus (the Swan)
approximately 10 000 light years away in our Galaxy, the Milky Way.
The elegant technique, first suggested by Titarchuk in 1998, shows that
Cygnus X-1, part of a binary system, contains 8.7 solar masses, with a
margin of error of only 0.8 solar masses. Cygnus X-1 was one of the first
compelling black hole candidates to emerge in the early 1970s. The system
consists of a blue supergiant and a massive but invisible companion.
Alternative techniques have previously suggested that the invisible object
was a black hole of about 10 solar masses. "This agreement gives us a lot of
confidence that our method works," says Shaposhnikov. It can help determine
a black hole's mass when alternative techniques fail," adds Titarchuk.
Working independently from Shaposhnikov and Titarchuk, Tod Strohmayer and
Richard Mushotzky, also from GSFC, and four colleagues, used Titarchuk's
technique on XMM data and stumbled upon an Intermediate Mass Black Hole
(IMBH) -- the existence of which is in theory controversial.
They estimated that an ultraluminous X-ray source in the nearby galaxy, NGC
5408, harbours a black hole with a mass of about 2 000 Suns."This is one of
the best indications to date for an IMBH," says Strohmayer.
The existence of IMBHs is controversial because there is no widely accepted
mechanism for how they could form. But they would fill in a huge gap between
black holes such as Cygnus X-1 -- which form from collapsing massive stars
and contain perhaps 5 to 20 solar masses -- and the 'monsters' (up to
thousand million solar masses) that lurk in the cores of large galaxies.
Titarchuk's method takes advantage of a relationship between a black hole
and its surrounding accretion disk. Gas orbiting in these disks eventually
spirals into the black hole. When a black hole's accretion rate increases to
a high level, material piles up near the black hole in a hot region that
Titarchuk likens to a traffic jam.
Titarchuk has shown that the distance from the black hole where this
congestion occurs scales directly with the mass of the black hole. The more
massive the black hole, the farther this congestion occurs and the longer
the orbital period.
In his model, hot gas piling up in the congestion region is linked to
observations of X-ray intensity variations that repeat on a nearly, but not
perfectly, periodic basis. These Quasi-Periodic Oscillations (QPOs) are
observed in many black hole systems. The QPOs are accompanied by simple,
predictable changes in the system's spectrum as the surrounding gas heats
and cools in response to the changing accretion rate.
Precise timing observations from NASA's Rossi X-ray Timing Explorer (RXTE)
satellite have shown a close relationship between the frequency of QPOs and
the spectrum, telling astronomers how efficiently the black hole is
producing X-rays.
Using RXTE, Shaposhnikov and Titarchuk have applied this method to three
stellar-mass black holes in the Milky Way and shown that the derived masses
from the QPOs concur with mass measurements from other techniques.
Using ESA's XMM-Newton X-ray observatory, Strohmayer, Mushotzky, and their
colleagues detected two QPOs in NGC 5408 X-1.
NGC 5408 X-1 is the brightest X-ray source in the small, irregular galaxy
NGC 5408, 16 million light years from Earth in the constellation Centaurus.
The QPO frequencies, as well as the luminosity and spectral characteristics
of the source, imply that it is powered by an IMBH.
"We had two other ways of estimating the mass of the black hole, and all
three methods agree within a factor of two," says Mushotzky. "We don't have
proof this is an IMBH, but the preponderance of evidence suggests that it
is."
One of the study's coauthors, Roberto Soria of the Harvard-Smithsonian
Center for Astrophysics, thinks the black hole's mass is closer to one
hundred Suns.
Notes for editors
The findings described in this article will appear in two papers to be
published in the Astrophysical journals.
The first, "Quasi-Periodic Variability in NGC 5408 X-1", is by T.Strohmayer,
R.Mushotzky, L. Winter, R. Soria, P. Uttley, M. Cropper.
The second paper, "Determination of Black Hole Mass in Cyg X-1 by Scaling of
Spectral Index-QPO Frequency Correlation", is by N. Shaposhnikov and
L.Titarchuk.
For more information
Tod Strohmayer, NASA Goddard Space Flight Center, USA
Email: stroh @ milkyway.gsfc.nasa.gov
Nikolai Shaposhnikov, NASA Goddard Space Flight Center, USA
Email: nikolai @ milkyway.gsfc.nasa.gov
Norbert Schartel, ESA XMM-Newton Project Scientist
Email: norbert.schartel @ sciops.esa.int
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaCP/SEMDMAV681F_index_1.html ]
http://www.esa.int
16 May 2007
New technique for 'weighing' black holes
ESA's XMM-Newton has helped to find evidence for the existence of
controversial Intermediate Mass Black Holes. Scientists used a new, recently
proven method for determining the mass of black holes.
Nikolai Shaposhnikov and Lev Titarchuk, at NASA's Goddard Space Flight
Center (GSFC), have used the technique to determine the mass of the black
hole, Cygnus X-1, located in the constellation Cygnus (the Swan)
approximately 10 000 light years away in our Galaxy, the Milky Way.
The elegant technique, first suggested by Titarchuk in 1998, shows that
Cygnus X-1, part of a binary system, contains 8.7 solar masses, with a
margin of error of only 0.8 solar masses. Cygnus X-1 was one of the first
compelling black hole candidates to emerge in the early 1970s. The system
consists of a blue supergiant and a massive but invisible companion.
Alternative techniques have previously suggested that the invisible object
was a black hole of about 10 solar masses. "This agreement gives us a lot of
confidence that our method works," says Shaposhnikov. It can help determine
a black hole's mass when alternative techniques fail," adds Titarchuk.
Working independently from Shaposhnikov and Titarchuk, Tod Strohmayer and
Richard Mushotzky, also from GSFC, and four colleagues, used Titarchuk's
technique on XMM data and stumbled upon an Intermediate Mass Black Hole
(IMBH) -- the existence of which is in theory controversial.
They estimated that an ultraluminous X-ray source in the nearby galaxy, NGC
5408, harbours a black hole with a mass of about 2 000 Suns."This is one of
the best indications to date for an IMBH," says Strohmayer.
The existence of IMBHs is controversial because there is no widely accepted
mechanism for how they could form. But they would fill in a huge gap between
black holes such as Cygnus X-1 -- which form from collapsing massive stars
and contain perhaps 5 to 20 solar masses -- and the 'monsters' (up to
thousand million solar masses) that lurk in the cores of large galaxies.
Titarchuk's method takes advantage of a relationship between a black hole
and its surrounding accretion disk. Gas orbiting in these disks eventually
spirals into the black hole. When a black hole's accretion rate increases to
a high level, material piles up near the black hole in a hot region that
Titarchuk likens to a traffic jam.
Titarchuk has shown that the distance from the black hole where this
congestion occurs scales directly with the mass of the black hole. The more
massive the black hole, the farther this congestion occurs and the longer
the orbital period.
In his model, hot gas piling up in the congestion region is linked to
observations of X-ray intensity variations that repeat on a nearly, but not
perfectly, periodic basis. These Quasi-Periodic Oscillations (QPOs) are
observed in many black hole systems. The QPOs are accompanied by simple,
predictable changes in the system's spectrum as the surrounding gas heats
and cools in response to the changing accretion rate.
Precise timing observations from NASA's Rossi X-ray Timing Explorer (RXTE)
satellite have shown a close relationship between the frequency of QPOs and
the spectrum, telling astronomers how efficiently the black hole is
producing X-rays.
Using RXTE, Shaposhnikov and Titarchuk have applied this method to three
stellar-mass black holes in the Milky Way and shown that the derived masses
from the QPOs concur with mass measurements from other techniques.
Using ESA's XMM-Newton X-ray observatory, Strohmayer, Mushotzky, and their
colleagues detected two QPOs in NGC 5408 X-1.
NGC 5408 X-1 is the brightest X-ray source in the small, irregular galaxy
NGC 5408, 16 million light years from Earth in the constellation Centaurus.
The QPO frequencies, as well as the luminosity and spectral characteristics
of the source, imply that it is powered by an IMBH.
"We had two other ways of estimating the mass of the black hole, and all
three methods agree within a factor of two," says Mushotzky. "We don't have
proof this is an IMBH, but the preponderance of evidence suggests that it
is."
One of the study's coauthors, Roberto Soria of the Harvard-Smithsonian
Center for Astrophysics, thinks the black hole's mass is closer to one
hundred Suns.
Notes for editors
The findings described in this article will appear in two papers to be
published in the Astrophysical journals.
The first, "Quasi-Periodic Variability in NGC 5408 X-1", is by T.Strohmayer,
R.Mushotzky, L. Winter, R. Soria, P. Uttley, M. Cropper.
The second paper, "Determination of Black Hole Mass in Cyg X-1 by Scaling of
Spectral Index-QPO Frequency Correlation", is by N. Shaposhnikov and
L.Titarchuk.
For more information
Tod Strohmayer, NASA Goddard Space Flight Center, USA
Email: stroh @ milkyway.gsfc.nasa.gov
Nikolai Shaposhnikov, NASA Goddard Space Flight Center, USA
Email: nikolai @ milkyway.gsfc.nasa.gov
Norbert Schartel, ESA XMM-Newton Project Scientist
Email: norbert.schartel @ sciops.esa.int
[NOTE: Images and weblinks supporting this release are available at
http://www.esa.int/esaCP/SEMDMAV681F_index_1.html ]