The picture of the black hole the most important photo in history of astrophysics – Stuff.co.nz


The gravitational field of a black hole pulls in anything that ventures too close, including stars, planets and asteroids.

NASA

The gravitational field of a black hole pulls in anything that ventures too close, including stars, planets and asteroids.

In 1781 French astronomer Charles Messier published a catalogue of 103 rather fuzzy objects he thought were nebulae; the 87th object is M87.

Today we know this to be one of the most massive galaxies in our part of the Universe, situated at a distance of 54 million light years from Earth.

M87 has just become one of the most important objects in astronomical history. The engine room at the centre of this galaxy is a super massive black hole, 6.5 billion times more massive than our Sun and more than 1,600 times more massive than the black hole at the centre of our galaxy the Milky Way.

Scientist Roger Hanson says black holes remain mysterious.

SIMON O’CONNOR/STUFF

Scientist Roger Hanson says black holes remain mysterious.

In physics, mass refers to the number of particles not to the dimensions; a small but very dense object can be described as massive.

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A black hole is an object with an escape velocity greater than the speed of light – escape velocity is the speed required to escape from its gravitational grip.

The more mass packed into a given volume, the higher the escape velocity. The Earth’s escape velocity is 11.2kms/s whereas that of a black hole is more than 300,000kms/s, the speed of light, A gravitational pull that powerful, needs an enormous amount of mass.

The black hole at the centre of the Milky Way is about the size of the orbit of the planet closest to our Sun, Mercury, “small” by astronomical standards.

Black holes are extremely difficult to photograph because the galaxies containing super massive black holes are located at vast distances from Earth.

The gravitational field of a black hole pulls in anything that ventures too close, including stars, planets and asteroids.

The material near the black hole is moving at tens of thousands of kilometres per second as it spirals into the black hole.

Friction generated in this region around a black hole, called the accretion disk, generates temperatures of tens of million of degrees and emits electromagnetic radiation.

Until April 10, 2019 black holes were theoretical objects; however there was strong evidence of their existence.

The European Southern Observatory telescope tracked stars and gas orbiting very fast around what was assumed to be the black hole at the centre of our galaxy.

But seeing is believing and until a good image of a dark circle at the centre of a galaxy had actually been obtained, there would always be a nagging doubt about the existence of black holes.

On April 10 the first ever picture of a black hole, that at the centre of the M87 galaxy was obtained, it is the most important photograph in the history of astrophysics.

The image was obtained by combining data from eight telescopes located on four continents.

Using a technique called Large Array Baseline Interferometry, it is possible to construct a telescope which is for all intents and purposes the size of the Earth.

To do this, on April 4, 2017 each of the telescopes was pointed at M87 and began receiving the radio signals precisely at the same time.

This went on for a week after which vast amounts of data from each telescope were flown to two processing centres to be analysed.

Each of the telescopes on its own could not produce a distinct image, but by carefully combining data from each, an image could be assembled.

Vox Observatory video TV reported that four teams independently analysed the data to produce the photograph and that each came up with the same result, proving the analysis was correct.

Vox also noted why M87 was chosen; it is visible to all eight telescopes simultaneously once per year and it emits radio waves which can be received by Earth bound telescopes.

Luck was required for the experiment to be successful, the light from M87 had to pass unobstructed by dust, gas or large objects on its 54 million year journey.

One of the telescopes was situated in Antarctica; and the team had to wait six months for the large number of hard discs of data to be flown out since there are no winter flights from the continent.

Black holes remain mysterious; what is going on inside them, is there a point of infinite density (the singularity), are they gateways to new universes?

These are questions for future scientists to answer.



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