A definitive test for Black Holes?
Researchers believe it is so
Report by
R.Adm. RM Wey
OSR: SFS – SFC
Until recently, astronomers on the hunt for black holes relied on techniques of detection that were indirect in their approach, often leading to confusing possible objects with neutron stars.
As neutron stars of one solar mass have the same radius [approximately 30 km] as the ‘event horizon’ that defines a Black Hole of ten solar masses, such detection methods cannot often distinguish between the two.
One discernible difference is that neutron stars possess hard surfaces on which matter can accumulate, black holes…do not. It was this that led to the acknowledgment of a subtle difference in the radiation emitted from the vicinity of each body. In turn, providing researchers with a means to prove that such stellar phenomenon actually do exist.
One of the few properties not lost to matter that enters the event horizon of a black hole is angular momentum, this appears not in a manner seen directly, but as a ‘warp’ in the ‘space-time’ near its horizon. It is this momentum which propels ‘collisions’ within the event horizon, creating a large discharge of x-rays.
It is the very pattern observed in certain x-ray Binary star groups. As the brightest objects in the sky, it is reasoned that such stellar objects are companioned with an ‘unseen’ object.
Some of these
systems have been only seen once, emitting a burst of x-rays equal to one hundred thousand times the output of Earth’s sun.As no one has ever determined the exact temperature of a x-ray binary, inferences have been necessary. Through indirect means, it has been quantified at 107 degrees [consistent with that as determined for a black hole]. To account for the emissions, which have been observed, an object would need to consume some 10-9 to 10-8 solar masses in a year. It has thus been concluded that, such x-ray binaries could be the example of proof that such entities truly exist.
However, such arguments could just as easily be applied to a neutron star. Indeed, it is the evidence of magnetic fields, which a true black hole would need to lack, that point away from their existence in many cases. Any form of regular and steady pulsation would also rule out such a possibility. Be the reverse of such does not hold.
The absence of such bursts does not automatically mean a black hole either. But black holes have two properties that signify their presence: 1) Lack of a hard surface, and, 2) Their unlimited mass. There is not yet, however, a principle of physics to determine just how massive a black hole CAN be. Objects such as neutron stars do have a limit as to how massive THEY can become.
This is because an objects mass is limited by its ability to hold up under its own weight. Under the Pauli exclusion principle, there is a limit as to the number of fermions [one of the two classes of elementary particles] that can be packed into a given space. Exceeding this number generates an outward pressure against the gravity pulling it inward, while at the same time ‘increasing’ the stellar bodies mass.
Neutron stars are categorized as objects of ‘less’ than 2 solar masses, and the increasing pressure can sometimes cause the ‘failed’ star to continue its collapse, resulting in a black hole [such objects are larger than 3 solar masses]. In Binary systems, measurements of the speeds of the stellar objects and the use of Kepler’s laws of orbital motion have shown that seven x-ray transient Binaries meet the criteria to be considered black holes.
Some of these, notably Cygnus X-1, and GRO J1655-40, are to be given greater scrutiny by the orbiting x-ray observatories, Chandra, and XMM, shedding new ‘light’ on a dark subject.