---

VLBA observations key to 'complete description' of black hole

November 18, 2011

Precise distance measurement allowed calculation of mass, spin rate

For the first time, astronomers have produced a complete description of a black hole, a concentration of mass so dense that not even light can escape its powerful gravitational pull. Their precise measurements have allowed them to reconstruct the history of the object from its birth some six million years ago.

Using several telescopes, both ground-based and in orbit, the scientists unravelled longstanding mysteries about the object called Cygnus X-1, a famous binary-star system discovered to be strongly emitting X-rays nearly a half-century ago. The system consists of a black hole and a companion star from which the black hole is drawing material. The scientists' efforts yielded the most accurate measurements ever of the black hole's mass and spin rate.

"Because no other information can escape from a black hole, knowing its mass, spin, and electrical charge gives a complete description of it," said Mark Reid, of the Harvard-Smithsonian Center for Astrophysics (CfA). "The charge of this black hole is nearly zero, so measuring its mass and spin make our description complete," he added.

Though Cygnus X-1 has been studied intensely since its discovery, previous attempts to measure its mass and spin suffered from lack of a precise measurement of its distance from Earth. Reid led a team that used the National Science Foundation's Very Long Baseline Array (VLBA), a continent-wide radio-telescope system, to make a direct trigonometric measurement of the distance. Their VLBA observations provided a distance of 6070 light-years, while previous estimates had ranged from 5800-7800 light-years.

Armed with the new, precise distance measurement, scientists using the Chandra X-Ray Observatory, the Rossi X-Ray Timing Explorer, the Advanced Satellite for Cosmology and Astrophysics, and visible-light observations made over more than two decades, calculated that the black hole in Cygnus X-1 is nearly 15 times more massive than our Sun and is spinning more than 800 times per second.

"This new information gives us strong clues about how the black hole was born, what it weighed and how fast it was spinning," Reid said. "Getting a good measurement of the distance was crucial," Reid added.

"We now know that Cygnus X-1 is one of the most massive stellar black holes in the Milky Way," said Jerry Orosz, of San Diego State University. "It's spinning as fast as any black hole we've ever seen," he added.

In addition to measuring the distance, the VLBA observations, made during 2009 and 2010, also measured Cygnus X-1's movement through our Galaxy. That movement, the scientists, said, is too slow for the black hole to have been produced by a supernova explosion. Such an explosion would have given the object a "kick" to a much higher speed.

"There are suggestions that this black hole could have been formed without a supernova explosion, and our results support those suggestions," Reid said.

Reid, Orosz, and Lijun Gou, also of CfA, were the lead authors of three papers on Cygnus X-1 published in the Astrophysical Journal Letters.

The VLBA, dedicated in 1993, uses ten, 25-meter-diameter dish antennas distributed from Hawaii to St. Croix in the Caribbean. It is operated from the NRAO's Domenici Science Operations Center in Socorro, NM. All ten antennas work together as a single telescope with the greatest resolving power available to astronomy. This unique capability has produced landmark contributions to numerous scientific fields, ranging from Earth tectonics, climate research, and spacecraft navigation to cosmology.

Ongoing upgrades in electronics and computing have enhanced the VLBA's capabilities. With improvements now nearing completion, the VLBA will be as much as 5,000 times more powerful as a scientific tool than the original VLBA of 1993.

###

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

National Radio Astronomy Observatory

Related Black Hole Current Events and Black Hole News Articles

High-energy astrophysics puzzle
Blazars are the brightest of active galactic nuclei, and many emit very high-energy gamma rays. New observations of a blazar known as PKS 1424+240 show that it is the most-distant known source of very high-energy gamma rays. But its emission spectrum appears highly unusual.

University of Toronto-led study provides new insight into photosynthesis
Pigments found in plants and purple bacteria employed to provide protection from sun damage do more than just that.

Supernova remnant 1987A continues to reveal its secrets
A team of astronomers led by the International Centre for Radio Astronomy Research (ICRAR) have succeeded in observing the death throws of a giant star in unprecedented detail.

'Sideline quasars' helped to stifle early galaxy formation, says CU-Boulder study
University of Colorado Boulder astronomers targeting one of the brightest quasars glowing in the universe some 11 billion years ago say "sideline quasars" likely teamed up with it to heat abundant helium gas billions of years ago, preventing small galaxy formation.

Extremely rare triple quasar found
For only the second time in history, a team of scientists--including Carnegie's Michele Fumagalli--have discovered an extremely rare triple quasar system. Their work is published by Monthly Notices of the Royal Astronomical Society.

Curtains down for the black hole firewall paradox
Research by scientists at the University of York has revealed new insights into the life and death of black holes.

CSI: Milky Way
These days the core of the Milky Way galaxy is a pretty tame place...cosmically speaking. The galactic black hole at the center is a sleeping giant.

Supermassive black hole spins super-fast
Imagine a sphere more than 2 million miles across - eight times the distance from Earth to the Moon - spinning so fast that its surface is traveling at nearly the speed of light. Such an object exists: the supermassive black hole at the center of the spiral galaxy NGC 1365.

Journey to the Limits of Spacetime
Voracious absences at the center of galaxies, black holes shape the growth and death of the stars around them through their powerful gravitational pull and explosive ejections of energy.

Gas promises bumper black hole 'weigh-in'
A new way of measuring the mass of supermassive black holes could revolutionise our understanding of how they form and help to shape galaxies.

---

More Black Hole Current Events and Black Hole News Articles

---