Did Black holes and the prospects measuring gravitational waves? - Physics-Astronomy.org

Did Black holes and the prospects measuring gravitational waves?

The Huge  black holes found at the centre of every galaxy, including our own Milky Way, may, on average, be smaller than we thought, according to work led by University of Southampton astronomer Dr Francesco Shankar. If he and his colleagues are right, then the gravitational waves produced when they merge will be harder to detect than previously assumed. The international team of scientists publish their result in Monthly Notices of the Royal Astronomical Society
> .Black holes play a fundamental role in astronomy, gravitation, and particle physics. They are enormously concentrated masses, sometimes millions to billions of times more massive than the Sun, and have gravitational fields that are so powerful that not even light travels fast enough to escape their grasp, hence the name ‘black hole’.
Supermassive black holes have been found lurking in the cores of all galaxies observed with high enough sensitivity. Despite this, little is known about how they formed. What is known is that the mass of a Huge black hole at the centre of a galaxy is related to the total mass and the typical speeds (the "velocity dispersion") of the stars in its host.

The very existence of this relationship suggests a close co-evolution between black holes and their host galaxies, and understanding their origin is vital for a proper model of how galaxies and black holes form and evolve. This is because many galaxy evolution models invoke powerful winds and/or jets from the central  Huge black hole to control or even stop star formation in the host galaxy (so-called "quasar feedback"). Alternatively, multiple mergers of galaxies - and their central black holes - are also often suggested as the primary drivers behind the evolution of massive galaxies.

Despite major theoretical and observational efforts in the last decades, it remains unclear whether quasar feedback actually ever occurred in galaxies, and to what extent mergers have truly shaped galaxies and their black holes. Some of this is because modellers have had a tough time reproducing the observed black-hole galaxy scaling relations, and in reconciling the properties of nearby black holes with more distant populations.

The new work shows that selection effects – where what is observed is not representative - have significantly biased the view of the local black hole population. This bias has led to significantly overestimated black hole masses. It suggests that modellers should look to velocity dispersion rather than stellar mass as the key to unlocking the decades-old puzzles of both quasar feedback and the history of galaxies.

With less mass than previously thought, super-massive black holes have on average weaker
gravitational fields. Despite this, they were still able to power quasars, making them bright enough to be observed over distances of billions of light years.

Unfortunately, it also implies a substantial reduction in the expected gravitational wave signal detectable from pulsar timing array experiments. Ripples in spacetime that were first predicted by Albert Einstein in his general theory of relativity in 1915; gravitational waves were finally detected last year and announced by the LIGO team this February. The hope is that coming observatories can observe many more gravitational wave events, and that it will provide astronomers with a new technique for observing the universe.
Did Black holes and the prospects measuring gravitational waves?

No comments

Powered by Blogger.