Image: Artist's impression of stellar black hole
ESO/L. Calçada
Combining observations done with ESO's Very Large Telescope and NASA's Chandra X-ray telescope, astronomers have uncovered the most powerful pair of jets ever seen from a stellar black hole. The black hole blows a huge bubble of hot gas, 1,000 light-years across or twice as large and tens of times more powerful than the other such microquasars. The stellar black hole belongs to a binary system as pictured in this artist’s impression.
updated 7/7/2010 5:21:11 PM ET 2010-07-07T21:21:11

A newfound black hole has been caught in the act of releasing a prodigious amount of energy from the most powerful pair of jets ever seen from such a cosmic object. But the real surprise is what is created by those jets.

Astronomers noticed that the strong jets from this specific type of black hole, called a microquasar, are slamming into the surrounding interstellar gas, heating it and creating a massive bubble of hot gas that is 1,000 light-years across.

Microquasars are black holes that are also known as X-ray binaries, with jets of high-speed particles being a chief characteristic. Some microquasars have been known to produce gas bubbles due to the interaction of the jets with the surrounding interstellar medium, but these bubbles are typically relatively small — less than 10 light-years across.

This newly observed gas bubble is twice as large and tens of times more powerful than other known microquasars.

"We have been astonished by how much energy is injected into the gas by the black hole," said the study's lead author Manfred Pakull of the University of Strasbourg in France. "This black hole is just a few solar masses, but is a real miniature version of the most powerful quasars and radio galaxies, which contain black holes with masses of a few million times that of the sun."

The surprising discovery was made using the European Southern Observatory's Very Large Telescope and NASA's Chandra X-ray telescope. The findings are published in this week's issue of the journal Nature.

All about black holes
The gas-blowing black hole is located 12 million light-years away, in the outskirts of the spiral galaxy NGC 7793. Judging by the size and expansion velocity of the gas bubble, the researchers have calculated that the jet activity must have been ongoing for at least 200,000 years.

Black holes are known to release enormous amounts of energy when they gobble up matter. It was commonly believed that most of the energy was released in the form of radiation – predominantly X-rays.

This new discovery, however, shows that some black holes can release at least as much energy (and perhaps much more) in the form of collimated jets of fast-moving particles. These jets heat the surrounding interstellar gas, triggering an expansion. The inflating bubble that results contains a mixture of hot gas and ultra-fast particles at different temperatures.

"In microquasars the black hole has a companion star, it forms a binary star," Pakull told "If the companion star is sufficiently big, it loses material which can fall onto the black hole. During that process (which we call accretion), the potential energy of the material is converted into heat and radiation that we observe as X-rays."

Some of that potential energy can also be converted into kinetic energy, he added. That's where the black hole jets come in.

"In our object, most of the energy is indeed converted into jets, and very little into X-ray radiation," Pakull said.

Pakull and his team of astronomers used observations in optical, radio and X-ray bands to calculate the total rate at which the black hole is heating its surroundings.

A closer look at the jets
The researchers examined the spots where the jets smash into the interstellar gas located around the black hole, and were able to determine that the bubble of hot gas is inflating at a staggering speed of almost one million kilometers per hour.

"The length of the jets in NGC 7793 is amazing, compared to the size of the black hole from which they are launched," said co-author Robert Soria of the Mullard Space Science Laboratory at the University College London. "If the black hole were shrunk to the size of a soccer ball, each jet would extend from the Earth to beyond the orbit of Pluto."

At the moment, the astronomers are not able to measure the size of the black hole itself.

The smallest stellar black hole discovered so far has a radius of about 9.3 miles (15 km). An average stellar black hole of about 10 solar masses has a radius of about 18.6 miles (30 km). In comparison, a "big" stellar black hole may have a radius of up to 186 miles (300 km).

Yet, these large black holes are still smaller than the jets, which extend out to several hundred light-years on each side of the black hole.

The findings of this study will help astronomers understand the similarity between small black holes formed from exploded stars and the supermassive black holes that are located at the centers of galaxies.

Powerful jets have been observed from supermassive black holes, but they were thought to be less frequent in the smaller microquasar variety. The study suggests that perhaps many of them have simply gone unnoticed so far.

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