When Einstein developed relativity theory, he found a new way to describe gravity. It took him years to work out the math to find the solutions to his own equations, but they were only an approximate solution. The first complete solution to Eintstein’ unfinished equations was found by a theoretical physicist named Karl Schwarzschild in 1916. Significantly, Schwarzschild’ solution provided support for an extreme situation about the effects of severely compressed matter on gravity and energy.
If an object have sufficiently compact mass then it can deform spacetime to form a strange but a fascinating thing called black hole, a region of spacetime with extreme density and zero-volume but all of its mass as a singularity — I know its hard to imagine something like black holes, don’t worry, even the thinkers of that period could not imagine it, the idea of a singularity troubled many scientists, even Einstein himself, he argued vigorously that black holes were incompatible with reality.
In his work published shortly before his death in 1916, Schwarzschild also explained that a singularity was surrounded by a spherical gravitational boundary in spacetime that forever trapped anything that ventured too close to it, nothing can escape from inside it, scientists refer to it as “the point of no return”. This boundary was named the event horizon. Schwarzschild also presented a formula that calculated the size of an event horizon-known as the Schwarzschild radius.
Until now we talk about some theoretical concepts of black holes but we never mentioned how a black hole born… So how do these strange objects form? Scientists say they are born when the center of a very massive star collapses in upon itself.
The vast majority of our contemporary scientists believe that black holes exist but there are also some skeptics. Stephen Hawking is one of them. In a paper posted online on the arXiv preprint server on 22 January, Hawking claims that the notion of an ‘event horizon’ is incompatible with quantum theory.
There is no escape from a black hole in classical theory,
Quantum theory, however, “enables energy and information to escape from a black hole.
In a nutshell, a black hole will never form because the gravitational energy required to create it (E=mc2) is greater than the equivalent energy of the mass.
The observer Dilemma
Every observer of a collapsing star will observe that the star will stop collapsing before crossing a critical radius (Schwarzschild radius) and becoming a black hole. However, an observer’s perception of the passage of time can vary significantly depending of the strength of the gravity field from which observations are made. From the perspective of a distant observer, the rate of collapse will slow down so much as the surface approaches the critical radius that the critical radius will never be crossed in finite time.
This was the inception of black stars’ concept. So, stars that are collapsing toward forming a black hole but are frozen near the Schwarzschild horizon are termed “black stars”. A Black Star is a theoretical object alternative to the black hole, composed of matter. In contrast, as we explained, a “black hole” is a vacuum solution of Einstein’s equations and there is no matter distribution inside it except for the singularity at the origin.
Black Stars Collisions
Collisions of black stars in contrast to black hole collisions may be sources of gamma ray bursts. Black star’ gamma ray bursts should be preceded by gravitational wave emission similar to that from the coalescence of black holes.
When black stars do collide, they can be distinguished from black holes by the nature of the radiation. The infall of matter on to a black star will also lead to electromagnetic emission due to collisions of the matter with the matter making up the black star. On the other hand, matter that is falling into a black hole will not emit electromagnetically except due to collision with other infalling matter, as in an accretion disk.
An extravagant claim: The black stars scenario
Recently LIGO has announced the discovery of gravitational waves that match the signal expected from the merger of two black holes, each of mass ~ 30 Sun’ masses. But soon after the LIGO event (0.4 s), Fermi has detected a gamma ray burst that is consistent with the interpretation of being an electromagnetic counterpart of the LIGO.
In a new paper published online on arxiv server on 16 March, Tanmay Vachaspati profesor at Arizona state university, discuss another explanation for Ligo event, claiming that the black star scenario qualitatively fits the LIGO+Fermi observations.
Although in his work, Vachaspati have found the black stars scenario is more suitable than the merger of 2 black holes, more accurate predictions and more observational data are expected in the near future to unravel this mystery.
We can never be sure if the gravitational signatures are from colliding primordial black holes or from black stars whose matter is yet to collide.
Study of black holes has always provoked a great variety of reactions from researchers. On the one hand, it is exciting to think that they hide within them the door to unforeseeable new possibilities in physics, albeit only for those who dare to enter. On the other hand, implications of black holes have long disturbed some physicists—the quest for alternatives to black holes.