Stars Dancing with Black Holes

Stars Dancing with Black Holes was the title of Marc Freitag’s talk at this months meeting of the Cambridge Astronomy Association.

Marc began by explaining what actually is defined as a black hole; known to have a most extreme case of gravitation, where the mass is concentrated in one point and it is surrounded by a spherical horizon.

Marc also had an interesting slide detailing the flow and gravity pull of a black hole which included details on subsonic flow, supersonic flow and about the sonic horizon.

There is believed to be a black hole at the centre of our Milky Way.

We were told that the effects of Massive Black Holes (MBH) on stars can be used to reveal the presence of Massive Black Holes and determine their properties. We also learnt that stars around Massive Black Holes in a spherical nucleus produce a rosette orbit and that as a star is close to an MBH you get a Keplerian ellipse.

Stellar Massive Black Holes are the end product of evolution of stars greater than 20 to 30 suns, and they are only 1-2 stars in 1,000.  This version accumulates around the Massive Black Holes.

One interesting future piece of research is to be the LISA spacecraft which is being designed to measure the mass and rotation of Massive Black Holes. IT will measure Gravitational Waves (GW) which are emitted when a black hole passes a massive black hole.

A Gravitational Wave is a contraction of space in one direction and an expansion in the other direction. Gravitational Waves also produce contraction and expansion of space itself.

The LISA spacecraft consist of three spacecraft that will form the shape of a triangle in space in an orbit similar to that of the earth.  The distance between the spacecraft will be 5 million km apart.

LISA will detect gravitation waves by comparing distances between “test masses” in different directions using lasers. A similar research project on the ground has been executed called LIGO in the US and VIRGO in Italy.

Overall the talk was very in depth and I got a bit lost half way through with all of the formulae and physics, but the talk was littered with interesting images, simulations and videos.

I look forward to see the launch of LISA in the future, and to see if it will be possible to detect gravitational waves as well as if it will be possible to keep the three spacecraft evenly spaced across space in order to constantly create a perfect triangle.

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