(ORDO NEWS) — A relatively small, dense object hidden in a cloud of its own exploding remains, just a few thousand light-years away, challenges our understanding of stellar physics.
The general consensus is that it is a neutron. a star, albeit an unusual one. With a mass of just 77 percent that of the Sun, it is the lowest mass ever measured for an object of its kind.
Previously, the lightest neutron star ever measured had a mass 1.17 times that of the Sun.
This recent discovery is not only smaller, it is significantly smaller than the minimum neutron star mass predicted by theory.
This suggests that either there is some gap in our understanding of these superdense objects … or we are not seeing a neutron star at all, but a peculiar, never before observed object known as a “strange” star.
Neutron stars are among the densest objects in the universe. This is what remains after a massive star, about 8 to 30 times the mass of the Sun, has reached the end of its life.
When a star runs out of material needed to fuse at its core, it goes supernova, ejecting the outer layers of material into space.
No longer supported by external fusion pressure, the nucleus collapses on its own to form an object so dense that the atomic nuclei are compressed together and the electrons are forced to approach the protons long enough to become neutrons.
Most of these compact objects are about 1.4 times the mass of the Sun, although theory says they can range from something as massive as about 2.3 solar masses to as little as 1.1 solar masses.
It’s all packed inside a sphere, freshly packed into a sphere only 20 kilometers (12 miles) in diameter, resulting in each teaspoon of neutron star matter weighing anywhere from 10 million to several billion tons.
Stars with higher and lower masses than neutron stars can also turn into dense objects. Heavier stars turn into black holes.
Lighter stars turn into white dwarfs – less dense than neutron stars, with an upper mass limit of 1.4 solar masses, but still quite compact. Such is the possible fate of our own Sun.
The neutron star that is the subject of this study lies at the center of a supernova remnant called HESS J1731-347, which was previously thought to be more than 10,000 light-years away.
However, one of the difficulties in studying neutron stars lies in poorly constrained distance measurements. Without an accurate distance, it is difficult to obtain accurate measurements of the star’s other characteristics.
Recently, a second optically bright star has been discovered in HESS J1731-347. Based on this, using data from the Gaia mapping survey, a team of astronomers led by Viktor Doroshenko from the Eberhard Karl University of Tübingen in Germany were able to recalculate the distance to HESS J1731-347 and found that it was much closer than expected, around 8150 meters. at a distance of light years.
This means that previous estimates of other characteristics of the neutron star, including its mass, need to be refined.
Combined with observations of the neutron star’s X-ray emission (incompatible with the X-ray emission of a white dwarf), Doroshenko and his colleagues were able to refine its radius to 10.4 km and its mass to a staggeringly small 0.77 solar. masses.
This means that it may not actually be a neutron star as we know it, but a hypothetical object not yet identified in the wild.
“Our mass estimate makes the central compact object in HESS J1731-347, the lightest neutron star known to date, and a potentially more exotic object, that is, a candidate for “strange stars,” the researchers write in their paper.
According to the theory, a strange star is very similar to a neutron star, but contains a large proportion of fundamental particles called strange quarks.
Quarks are fundamental subatomic particles that combine to form compound particles such as protons and neutrons.
Quarks come in six different types or flavors: up, down, charming, weird, up, and down. Protons and neutrons are made up of up and down quarks.
The theory suggests that in the highly compressed environment inside a neutron star, subatomic particles break up into their constituent quarks.
According to this model, strange stars are composed of matter composed of equal proportions of up, down, and strange quarks.
Strange stars have to form at masses large enough to really compress, but since the rulebook for neutron stars is out of bounds when enough quarks are involved, there is essentially no lower limit either.
This means that we cannot rule out the possibility that this neutron star is actually a strange star.
It would be amazing; physicists have been looking for quark matter and strange quark matter for decades. However, while a strange star is certainly a possibility, it’s more likely that what we’re looking at is a neutron star, which is pretty cool too.
“The resulting mass and radius constraints are still fully consistent with the standard neutron star interpretation and can be used to improve astrophysical constraints on the equation of state for cold dense matter under this assumption,” the researchers write.
“Such a light neutron star, regardless of the proposed internal composition, appears to be a very intriguing object from an astrophysical point of view.”
It is difficult to establish how such a light neutron star could form according to our current models. So, whatever it’s made of, the dense object at the heart of HESS J1731-347 could tell us something about the mysterious afterlife of massive stars.
Contact us: firstname.lastname@example.org