Filed under: Technology | Tags: 4649, Astronomy, astrophysics, Black Hole, Chandra, Galaxy, NASA, NGC, Science, space, Space Technology, star, Suman, supermassive
How do you weigh the biggest black holes in the universe? One answer now comes from a completely new and independent technique that astronomers have developed using data from NASA’s Chandra X-ray Observatory.
By measuring a peak in the temperature of hot gas in the center of the giant elliptical galaxy NGC 4649, scientists have determined the mass of the galaxy’s supermassive black hole. The method, applied for the first time, gives results that are consistent with a traditional technique. Astronomers have been seeking out different, independent ways of precisely weighing the largest supermassive black holes, that is, those that are billions of times more massive than the Sun. Until now, methods based on observations of the motions of stars or of gas in a disk near such large black holes had been used. “This is tremendously important work since black holes can be elusive, and there are only a couple of ways to weigh them accurately,” said Philip Humphrey of the University of California at Irvine, who led the study.
NGC 4649 is now one of only a handful of galaxies for which the mass of a supermassive black hole has been measured with two different methods. In addition, this new X-ray technique confirms that the supermassive black hole in NGC 4649 is one of the largest in the local universe with a mass about 3.4 billion times that of the Sun, about a thousand times bigger than the black hole at the center of our galaxy. The new technique takes advantage of the gravitational influence the black hole has on the hot gas near the center of the galaxy. As gas slowly settles towards the black hole, it gets compressed and heated. This causes a peak in the temperature of the gas right near the center of the galaxy. The more massive the black hole, the bigger the temperature peak .
This effect was predicted by two of the co-authors — Fabrizio Brighenti from the University of Bologna, Italy, and William Mathews from the University of California at Santa Cruz — almost 10 years ago, but this is the first time it has been seen and used. The black hole in NGC 4649 is in a state where it does not appear to be rapidly pulling in material towards its event horizon, nor generating copious amounts of light as it grows. So, the presence and mass of the central black hole has to be studied more indirectly by tracking its effects on stars and gas surrounding it.
This technique is well suited to black holes in this condition. “Monster black holes like this one power spectacular light shows in the distant, early universe, but not in the local universe,” said Humphrey. “So, we can’t wait to apply our new method to other nearby galaxies harboring such inconspicuous black holes.” These results will appear in an upcoming issue of The Astrophysical Journal.
Filed under: Technology | Tags: Chandra Space Observatory, Milky Way, NASA, National Radio Astronomy Observatory, Science, Suman Das, Supernova
Before telling you about the latest supernova that had been discovered recently, Let me explain what exactly a Supernova is:
A supernova (plural: supernovae) is a stellar explosion. They are extremely luminous and cause a burst of radiation that often briefly outshines an entire galaxy before fading from view over several weeks or months. Each explosion ejects from one to several tens of solar masses at speeds ranging from thousands to tens of thousands of kilometers per second. The total kinetic energy, 1044 joules (2.5 × 1028 megatons of high explosive), is about 100 times the total light output, making supernovae some of the highest-energy explosions in the universe. The most recent supernova in our galaxy has been discovered by tracking the rapid expansion of its remains. This result, using NASA’s Chandra X-ray Observatory and the National Radio Astronomy Observatory’s Very Large Array, will help improve our understanding of how often supernovae explode in the Milky Way galaxy.
The supernova explosion occurred about 140 years ago, making it the most recent in the Milky Way. Previously, the last known supernova in our galaxy occurred around 1680, an estimate based on the expansion of its remnant, Cassiopeia A. Finding such a recent, obscured supernova is a first step in making a better estimate of how often the stellar explosions occur. This is important because supernovae heat and redistribute large amounts of gas, and pump heavy elements out into their surroundings. They can trigger the formation of new stars as part of a cycle of stellar death and rebirth. The explosion also can leave behind, in addition to the expanding remnant, a central neutron star or black hole.
The recent supernova explosion was not seen with optical telescopes because it occurred close to the center of the galaxy and is embedded in a dense field of gas and dust. This made the object about a trillion times fainter, in optical light, than an un-obscured supernova. However, the remnant it caused can be seen by X-ray and radio telescopes.
Astronomers regularly observe supernovae in other galaxies like ours. Based on those observations, researchers estimated about three explosions every century in the Milky Way. The tracking of this object began in 1985, when astronomers, used the Very Large Array to identify the remnant of a supernova explosion near the center of our galaxy. Based on its small size, it was thought to have resulted from a supernova that exploded about 400 to 1000 years ago. Twenty-two years later, Chandra observations revealed the remnant had expanded by a surprisingly large amount, about 16 percent, since 1985. This indicates the supernova remnant is much younger than previously thought.
That young age was confirmed in recent weeks when the Very Large Array made new radio observations. This comparison of data pinpoints the age of the remnant at 140 years – possibly less if it has been slowing down – making it the youngest on record in the Milky Way. Besides being the record holder for youngest supernova, the object is of considerable interest for other reasons. The high expansion velocities and extreme particle energies that have been generated are unprecedented and should stimulate deeper studies of the object with Chandra and the Very Large Array. These results are scheduled to appear in The Astrophysical Journal Letters.
NASA’s Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA’s Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra’s science and flight operations from the Chandra X-ray Center in Cambridge, Mass.
