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Black holes influence galaxy evolution

EU-funded scientists have found that the gravitational well residing at the heart of a nearby galaxy radiates sufficient energy into local space to change the star formation rate.
Black holes influence galaxy evolution
The jets produced by supermassive black holes are known to heat up surrounding gas, making it impossible for birth clouds to condense and collapse into stars. In the EU-funded project BHS SHAPING GALAXIES (Black holes altering galaxy evolution: how to find them?), this effect has been witnessed in detail.

Scientists looked at the prototype galaxy IC 5063 and large outflows of gas. The gas is accelerated by the black hole jet, creating a wind stretching for over 2 200 light years, with velocities between 600 to 1 200 kilometres per second with respect to the motion of the galaxy. The effects of the radio jet of IC 5063 had been observed in the past. This very active galaxy is relatively close – 160 million light years from Earth. These two characteristics make it an ideal candidate to study the impact that supermassive black holes have on galaxies.

Another important feature of IC 5063 is that the radio jet is almost aligned with the gas disk in its centre. It is made of electrons sent on corkscrew orbits away from a black hole. These electrons emit synchrotron radiation, which excites and heats up the surrounding gas.

The radiation for the jet created bow shocks in the gas that is pushed into forming large, hot, fast winds in four distinct regions. The wind temperature is between 1500 to 2700 Kelvins and more than 2 million square light years are heated up.

Stars form after a hydrogen cloud collapses, until its weight forces hydrogen to fuse into helium and release energy. For the cloud to collapse, the gas needs to cool down and condense. But the winds observed heat up and disperse the gas, disrupting star formation.

The BHS SHAPING GALAXIES team also searched for such winds in data for radio galaxies collected by the Institut de radioastronomie millimétrique (IRAM) telescope and in active galactic nuclei observations from Herschel space telescope. Up to 50 % of the sources showed outflow signatures.

Current theories of galactic evolution are difficult to test since processes occur extremely slowly. By looking at radio jets from black holes, scientists have found evidence that these signal the end for star formation. Afterwards, galaxies tend to age, hardly forming any new stars.

A video titled 'Winds in the galaxy IC5063 driven by a black hole jet' is available here.

Related information

Keywords

Black holes, star formation, BHS SHAPING GALAXIES, radio jet, synchrotron radiation
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