Context: An object has been detected in the star clusterNGC 1851, whose mass (between 2.09 and 2.71 times the mass of the Sun) falls within the black hole mass gap.
Major Highlights:
Black Hole Mass Gap:
- Neutron stars are incredibly dense objects formed from the collapse of massive stars. Their maximum mass is thought to be around 2.2 solar masses.
- Black holes are even more massive, the lightest black holes are believed to be around 5 solar masses.
- Between these two ranges lies the "mass gap" - a region where no objects have been definitively identified.
- At the boundary between neutron stars and black holes there is always the possibility that some new, as yet unknown, astrophysical object might exist.
The Newly Discovered Object:
- This object resides in a binary system within the star cluster NGC 1851, roughly 40,000 light-years from Earth.
- Its companion is a millisecond pulsar, a rapidly spinning neutron star that emits regular pulses of radio waves.
- By studying the pulsar's orbital motion, astronomers have estimated the mass of the unknown object to be between 2.09 and 2.71 solar masses. This places it within the mass gap.
Neutron Stars:
- Neutron stars are the incredibly dense remnants of supermassive stars (with masses around 1025 times the mass of the Sun) that have exploded as supernovae.
- They are formed when massive stars undergo supernova explosions at the end of their lifecycle. During the explosion, the outer layers of the star are expelled into space, while the core collapses under its own gravity. The core becomes so dense that protons and electrons combine to form neutrons, hence the name "neutron star." Neutron stars do not have an event horizon.
- Supernovae are incredibly powerful explosions that occur when a massive supergiant star reaches the end of its life. These explosions release an astonishing amount of energy, up to 10^44 joules.
- They are formed when massive stars undergo supernova explosions at the end of their lifecycle. During the explosion, the outer layers of the star are expelled into space, while the core collapses under its own gravity. The core becomes so dense that protons and electrons combine to form neutrons, hence the name "neutron star." Neutron stars do not have an event horizon.
- Neutron stars are about 15-30 kms in diameter and have a mass between 1.4- 2.2 solar masses. They are the densest known stellar objects in the universe, second only to the black holes.
- They have breathtakingly high rotation speeds with rotational periods that can be just 0.3 to 12.0 seconds.
- They often possess extremely strong magnetic fields, much stronger than those of regular stars. These magnetic fields can give rise to intense radiation emissions, including beams of electromagnetic radiation and particle streams, which are observable as pulsars.
Black Holes:
- Black holes are regions of spacetime where gravity is so strong that nothing, including light and other electromagnetic waves, has enough energy to escape. The boundary of no escape is called the event horizon.
- The event horizon is the boundary surrounding a black hole from which it is impossible for matter or energy to escape the black hole's gravitational pull, i.e., the escape velocity at the event horizon is greater than the speed of light.
- It is formed when a dying star (leftover core) having more than three times the mass of the Sun undergoes a gravitational collapse, leading to the creation of a black hole.
- Stellar Black Hole: Formed by the collapse of a single massive star.
- Intermediate Black Hole: Masses between 100 and 1,00,000 times that of the sun.
- Supermassive Black Hole: Masses ranging from millions to billions of times that of the sun, found at the centres of most galaxies.
- Black holes are not directly observable. However, their presence can be inferred through their effects on surrounding matter and the gravitational waves they produce.
