India launched the X-ray Polarimeter Satellite (XPoSAT), the country's first mission to study black holes and neutron stars, on Monday, January 1. The 2024 New Year's Day mission is India's first dedicated polarimetry mission to study the dynamics of bright astronomical X-ray sources in extreme conditions. This means that the spacecraft will analyse X-ray sources of celestial bodies such as black holes, neutron stars, active galactic nuclei, and pulsar wind nebulae by measuring the beams of light in which the vibrations of the electromagnetic waves are confined to one plane.
The Indian Space Research Organisation (ISRO) launched XPoSAT into an eastward low-inclination orbit, atop a Polar Satellite Launch Vehicle (PSLV), as part of the PSLV-C58 mission, PSLV's 60th mission. XPoSAT blasted off into space at 9:10 am IST, from the First Launch Pad at Satish Dhawan Space Centre, Sriharikota.
The XPoSAT mission is the first mission, and the first orbital launch attempt of 2024, and ISRO's 92nd mission overall.
Black holes
Black holes are not really holes, but huge concentrations of matter packed into very tiny regions.
A black hole is a region in space-time which has such a strong gravitational pull that even light can’t escape it, and it engulfs all matter entering it.
Black holes are so dense that their strong gravitational pull does not allow anything, not even light, to escape.
The colossal behemoths engulf everything that comes within their vicinity. The accreting matter forms a disk around a black hole, and reflects radiation, making the structure visible.
The boundary of a black hole, that contains all the matter making up the colossal behemoth, is called the event horizon. It is not a surface like that of Earth or the Sun.
Nebula
A star is formed from the material present inside a nebula, which is a giant, diffuse cloud of dust and gas in space. The amount of matter present in a nebula determines the mass of a star. A nebula consists of gases such as hydrogen and helium, which are evenly spread out, but are pulled together by gravity.
White dwarf
A white dwarf is a star that has exhausted most of its nuclear fuel, and has collapsed to a very small size, usually a radius equal to about 0.01 times that of the Sun.
Supernova
A supernova can be the death explosion of a massive star, resulting in a sharp increase in brightness, followed by a gradual fading, or the explosion of a white dwarf which has accumulated enough material from a companion star to achieve a mass equal to the Chandrashekhar limit, which is the maximum mass theoretically possible for a stable white dwarf star. It is impossible for a white dwarf star to be stable if its mass is greater than 1.44 times the mass of the Sun.
Neutron star
A dying star with a mass greater than the Chandrashekhar limit either becomes a neutron star or a black hole.
The fate of the supernova remnant depends on its mass. The supernova remnant can either become a neutron star or a black hole, depending on its mass.
A neutron star is the imploded core of a massive star produced by a supernova explosion, and has a mass about 1.4 to three times that of the Sun, a radius of about eight kilometres, and the density of a neutron.
All supernovae leave behind a very dense core, and a nebula. Stars more than 10 times the size of the Sun produce black holes. In such cases, the supernova remnant is more than three times the mass of the Sun.
In the case of a black hole, the gravitational forces swallow the supernova remnant. The black hole accretes everything that comes in its vicinity.
However, when the supernova remnant is 1.4 to three times the mass of the Sun, it gets converted into a neutron star.
According to the National Radio Astronomy Observatory, a neutron star that is left over after a supernova is a remnant of the massive star which went supernova. Black hole formation can also occur without a supernova explosion, if the star is massive enough. This is because it will collapse directly in less than half a second.
The collapse of a neutron star can also result in the formation of a black hole if it accretes sufficient material from a nearby companion star, or merges with a companion star. The merging can increase the mass to an extent that the neutron star mass limit is crossed, and a black hole is formed. The mass limit of a neutron star is three solar masses.
Conversion of a neutron star into a black hole can take more than millions of years, depending on the rate of accretion of material. Once a neutron star crosses the mass limit of three solar masses, it collapses into a black hole in less than a second.
Active galactic nucleus
An active galactic nucleus is a small region at the centre of some galaxies that is extremely luminous, and emits so much radiation that it can outshine the rest of the galaxy altogether. Active galactic nuclei are now understood to be active supermassive black holes that emit bright jets and winds, and shape their galaxies.
Pulsars
Pulsars are rotating neutron stars observed to have pulses of radiation at very regular intervals that range from milliseconds to seconds, and have very strong magnetic fields which funnel jets of particles out along the two magnetic poles.
Pulsar wind nebula
A pulsar wind nebula is a phenomenon in which winds of particles travelling near the speed of light emerge from the surface of a pulsar, and create a chaotic concoction of charged particles and magnetic fields that crash into the surrounding gas, or nebula.
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