Neutron stars are formed from the explosion of massive stars 10 to 30 times heavier than our sun, also known as supernovae. This exorbitant cosmic inheritance is passed on to the newly-formed neutron star, rising from the ashes of the original star’s collapsed core.
With this in mind, there’s little wonder that neutron stars typically grow to have the combined mass of two suns put together, described as two solar masses.
But astronomers have recently discovered a supermassive neutron star weighing 2.3 solar masses, reports Gizmodo. Dubbed PSR J2215+5135, the newfound neutron star is one of the heaviest ever detected and is surpassed only by a 2.4-solar-mass neutron star described in an arXiv paper in 2010.
According to Gizmodo, such supermassive neutron stars are a rarity.
“Out of the approximately 2,000 neutron stars known to astronomers, only four are more than two solar masses,” states the media outlet.
But this rare supermassive neutron star, which turned out to be a “redback pulsar,” did not give up its secrets easily. Finding out the star’s mass proved to be a real challenge because PSR J2215+5135 resides in a compact binary system in which it’s closely orbited by a smaller stellar companion.
Because of the short distance between the two stars, the lower-mass companion is constantly blasted with X-rays by the fast-spinning neutron star, also known as a pulsar. This particular type of neutron star is called a “redback” pulsar, notes Gizmodo.
The outpour of radiation coming from the “redback” pulsar makes it hard to distinguish from its companion, which complicates the mass measurements for either of the two stars.
To calculate the neutron star’s mass, researchers from the Universitat Politecnica de Catalunya (UPC), in Barcelona, Spain, and the Canary Islands Institute of Astrophysics came up with a pioneering technique focused on speed rather than on weight.
This new method, described in a study published last week in the Astrophysical Journal, gauged the weight of the pulsar by looking at how fast its companion spins.
Knowing that the speed of the stellar companion increases with the pulsar’s mass, the team, led by UPC physicist Manuel Linares, used spectral lines of hydrogen and magnesium to measure the speed of the companion star, Heritage Daily reports.
The researchers imaged the double star system with four different telescopes from the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, Spain: the Gran Telescopio Canarias, which is the world’s the largest optical and infrared telescope, the William Herschel Telescope, the Isaac Newton Telescope, and the IAC-80 telescope.
The team then ran computer simulations of the binary star system and analyzed the patterns of the radiation which continuously batters the pulsar’s companion.
The technique allowed the researchers to measure the speeds of both sides of the companion star, the irradiated, hotter side and the shaded, cooler side. This has never been done before, notes Heritage Daily.
The calculations revealed both the temperature of the star at each of its two sides, as well as its velocity, found to be of 412 kilometers per second, or 921,618 miles per hour. This enabled the team to establish that the “redback” pulsar packs a tight mass of 2.3 solar masses.
This is truly remarkable, considering that pulsars are usually no bigger than a large town and are only 12 miles wide.
The new method has great potential for future applications and could be used to calculate the mass of black holes and white dwarf stars, both equally dense celestial objects.