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Dwarf Galaxy Could Be an Ejected Black Hole

By David Reneke

Astronomers have observed what could be a massive black hole that has been ejected into space after two galaxies collided.

Dwarf Galaxy Could Be an Ejected Black Hole

Astronomers have observed a mysterious phenomenon that could be a massive black hole that has been ejected into space in connection with two galaxies colliding. This may be due to gravitational waves from the collision.

If two galaxies are on a collision course and eventually collide, they will merge into a single larger galaxy. At the centre of each galaxy is a massive black hole and they will also merge. If gravitational waves have been formed in the process, spreading out into space, there might be a recoiling effect, causing one of the two black holes to be ejected.

In some cases, the recoil effect is relatively weak and the black hole is pulled back to the centre. In other cases, the recoil effect is so strong that the black hole is flung out of the galaxy forever.

Astronomers have long been searching for such recoil effects, and now they believe they’ve found one. It’s a black hole located 90 million light years from Earth, relatively close by.

An international team of researchers from the universities of Hawaii and Copenhagen have made observations with one of the largest telescopes in the world at the Keck Observatory in Hawaii. Using a technique called adaptive optics, which can compensate for disturbances from the atmosphere, it’s now possible to obtain precise observations with incredibly high resolution.

The observations show that an object called SDSS 1133 still has a ring of dust and gas drawing inwards as it emits radiation. The observations clearly show that there is no orbiting galaxy. “It appears that the black hole once belonged to a nearby dwarf galaxy before it was flung out,” explains Allison Man, a PhD student at the Dark Cosmology Centre at The University of Copenhagen.

Another possibility is that the object could be a special type of supernova – that is, an exploding massive star that can form a black hole. If this is the case it will be one of the most energy-rich and sustained explosions of a star that has ever been observed!

Researchers will observe the phenomenon over the next year using the Hubble Space Telescope’s Cosmic Origins Spectrograph, which can study the spectral lines of highly ionised carbon in active black holes. If this is a case of a supernova, the emission of light quickly becomes weaker. If it is a black hole that has been cast out of the galaxy it will emit light for a long time, perhaps millions of years.

A Call for a Giant Space Telescope

In the nearly 25 years since the launch of the Hubble Space Telescope (HST), astronomers and the public have enjoyed ground-breaking views of the cosmos and the suite of scientific discoveries that followed. The successor to HST, the James Webb Telescope, should launch in 2018 but will have a comparatively short lifetime.

Now Prof Martin Barstow of The University of Leicester is looking to the future. He calls for governments and space agencies around the world to back the Advanced Technologies Large Aperture Space Telescope (ATLAST), an instrument that would give scientists a good chance of detecting hints of life on planets around other stars.

ATLAST is currently a concept under development in the USA and Europe. Scientists and engineers envisage a telescope with a mirror as large as 20 metres across that, like HST, would detect visible light and also operate from the far ultraviolet to the infrared parts of the spectrum.

It would be capable of analysing the light from planets the size of the Earth in orbit around other nearby stars, searching for features like molecular oxygen, ozone, water and methane that could suggest the presence of life. It might also be able to see how the surfaces of planets change with the seasons.

ATLAST would study star and galaxy formation in high definition, constructing the history of star birth in detail and establishing how intergalactic matter was and is assembled into galaxies over billions of years.

ATLAST could be launched around 2030. Before this can happen there are technical challenges to overcome, such as enhancing the sensitivities of its detectors.

Such a large structure may also need to be assembled in space before deployment rather than launching it on a single rocket. All of this means that a decision to construct the telescope needs to happen soon for it to go ahead.

Since antiquity human beings have wondered whether we really are alone in the universe. ATLAST could finally allow us to answer this question. “The time is right for scientific and space agencies around the world, including those in the UK, to take a bold step forward and to commit to this project,” Barstow said.

David Reneke is an astronomy lecturer and teacher, a feature writer for major Australian newspapers and magazines, and a science correspondent for ABC and commercial radio.
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