March 2, 2014
By combining optical, X-ray and radio images, astronomers have discovered the size of black hole in MQ1 microquasar to be smaller than theorised based on the energy it emits via polar jets. This could change the way we think such small black holes influence evolution of galaxies.
Artist's impression of a microquasar. Small black hole on the right accretes gas from the regular star and ejects excess energy via two jets. Credit: T.D. Russell (ICRAR-Curtin), using BINSIM visualization code by R. Hynes (LSU)
Polar jets are formed when diffuse gas orbits a massive object, usually a black hole or a neutron star. This material creates an accretion disk that gets heated up as it rotates and feeds the black hole. Excess material gets ejected in two powerful jets, one on each pole of the central object, which have profound influence on the surrounding space, heating the gas and clearing it away, all this while emitting radiation in visible, X-ray and radio part of the electromagnetic spectrum.
A microquasar is a relatively small object, compared to a quasar, where a black hole is accreting material from a nearby star. Studying microquasars is important if we want to understand polar jets mentioned above. Since they are smaller than quasars, events involving microquasars happen on much smaller timescales, so we can study the nature of polar jets more often, their variations and how they affect their surroundings.
One such microquasar named MQ1, located near the centre of 15 million light-years distant spiral galaxy M83, was observed in the recent study. A group of Australian and American astronomers used the Hubble Space Telescope, the Chandra X-ray Observatory and the Australia Telescope Compact Array to find MQ1, by obtaining optical, X-ray and radio data, respectively.
"This powerful black hole is in a famous nearby galaxy that has been looked at gazillions of times, but was never spotted or never noticed," said Dr. Roberto Soria of International Centre for Radio Astronomy Research (ICRAR), Perth, Australia. He is study's lead author. "Only when you put all three images together does this black hole really stand out."
Compact objects with similarly powerful jets have been found before, but this is the first time that we were able to determine black hole's exact size. It turns out, the black hole in MQ1 is only 100 kilometers wide, but according to current theoretical models and based on the amount of radiation it emits, it was thought to be larger.
"The significance of the huge jet power measured for MQ1 goes beyond this particular galaxy: it helps astronomers understand and quantify the strong effect that black hole jets have on the surrounding gas, which gets heated and swept away," said Soria.
The discovery is important because it suggests an increased importance of small black holes on the evolution of young galaxies. Black holes that we ignored in the past because of their size deserve more attention in the future.
"This must have been a significant factor in the early stages of galaxy evolution, 12 billion years ago, because we have evidence that powerful black holes like MQ1, which are rare today, were much more common at the time," Soria added.