NASA’s Chandra X-Ray Observatory has observed a remarkable eclipse of a supermassive black hole.

The eclipse has allowed astronomers to measure the swirling disk of hot matter around the hole.

The black hole is located in NGC 1365, which is a spiral galaxy located some 60 million light years from Earth. This galaxy also contains an active galactic nucleus or AGN.

Astronomers believe that this AGN is fed by a steady stream of material from a surrounding disk। Matter is heated to millions of degrees before passing over the event horizon or the point of no return.

The disk of gas around the black hole is too small to be detected by a telescope. However this time the disk was eclipsed by a cloud passing by.

The team of researchers associated with Chandra has estimated the diameter of the X-ray source to be 7 AU or seven times the distance between Earth and Sun. If a black hole this size was present in our solar system it would have swallowed all planets up to Mars and all asteroids as well.

In addition to measuring the size of this disk of material, researchers were also able to estimate the location of the dense cloud that caused the eclipse. They have stated that the cloud is at a distance of a hundredth of a light year from the black hole’s event horizon. This is much closer than anyone ever expected. This is much of a puzzle for all astronomers.

Image Credit: NASA

black holes are the deadliest and most exiting aspect to the upcoming generations of scientists they are going to bring a huge amount of changes in the field of astronomical research abilities.

Black Holes and Critical Phenomena
A scalar field is a simple form of matter which feels two forces only, gravity produced by itself, and its own pressure. If you try to build a ball in which the field is initially weak, pressure wins and the ball expands away leaving nothing behind. If the field is initially strong gravity wins and the ball collapses to form a black hole

There is a special critical initial strength such that the field cannot decide whether to evaporate away or collapse to form a black hole. Instead it oscillates increasingly rapidly, performing an infinite number of oscillations in a finite time. The two animations show first an evolution which doesn't form a black hole, and second an evolution which does. The initial strengths differ only by one in the fifteenth decimal place. Each frame shows the scalar field as a function of position. The gravitational field changes the frequency of the field and so the colour indicates what a distant observer would see.

Movies

* This evolution doesn't form a black hole.
* This collapse does form a black hole.

Because the animation moves so quickly it is hard to see what is happening. The next picture summarises the animations.

Time is increasing from left to right (downwards).

Radius is increasing from left to right (upwards).

The colour indicates the curvature of spacetime. Far away (back of picture) the spacetime is almost flat (blue) while on the axis the field is becoming stronger and stronger (red turning black). Although there are an infinite number of oscillations in a finite time, all bunched up on each other, we have stretched out the time coordinate to separate them.

The next group of figures show the paths of photons emitted from the axis. Each blue line in the left picture represents a photon path. Radius is plotted horizontally and time vertically. Thus photons emitted at late times have higher lines in the figure. In the first picture there is some fine detail near the axis. the second increases the scale by one thousand, and the third by a further one thousand. Here you can see that all the photons escape.

The next set are the same photon paths but for the case where a black hole forms. At the finest resolution you can see that photons emitted at late times stop moving outwards and return back towards the axis. This is the moment at which the black hole forms.

This is an enlargement of the region where the black hole forms.

In the next picture we superpose the evolutions with (red) and without (green) black hole formation. At early times (bottom of the picture) the spacetimes differ only in the fifteenth decimal place. Once the spacetime decides what to do, the solutions then bifurcate.

BLACK HOLES




A massive star starts to collapse when it exhausts its nuclear fuel and can no longer counteract the inward pull of gravity.


The crushing weight of the star’s overlying layers implodes the core, and the star digs deeper into the fabric of space-time.


Although the star remains barely visible, its light now has a difficult time climbing out of the enormous gravity of the still-collapsing core.


The star passes through its event horizon and disappears from our universe, forming a singularity of infinite density.

OBSERVATIONAL EVIDENSE FOR BLACK HOLE

Dust disk around a black hole
This Hubble Space Telescope image contains three main features.
The outer white area is the core or centre of the galaxy NGC4261.
Inside the core there is a brown spiral-shaped disk. It weighs on hundred thousand times as much as our sun.
Because it is rotating we can measure the radii and speed of its constituents, and hence weigh the object at its centre. This object is about as large as our solar system, but weighs 1,200,000,000 times as much as our sun.
This means that gravity is about one million times as strong as on the sun. Almost certainly this object is a black hole.
Black hole in M87
M87 is an active galaxy, one in which we see interesting objects. Near its core (or centre) there is a spiral-shpaed disc of hot gas. The first picture places it in context. The second superposes spectra from opposite sides. This allows us to determine the speed of rotation of the disk and its size. From this we can weigh the size of the invisible object at the centre.
Although the object is no bigger than our solar system it weighs three billion times as much as the sun. This means that gravity is so strong that light cannot escape. We have a black hole.
In the first figure, there is a diagonal line. This is believed to be the passage out of those fortunate particles which escape along the axis of rotation and avoid being swallowed by the black hole.