Scientists Speculate That the Mysterious object is a "Strange Star" Made of Quarks.

 

(Pobytov/DigitalVision Vectors/Getty Images)

Our understanding of stellar physics is being challenged by a relatively small, dense object that is concealed within a cloud of its own exploded remains just a few thousand light-years away.

It appears to be a neutron star, albeit an unusual one from all accounts. It has the lowest mass ever measured for an object of its kind, at 77% of the Sun's mass.

The lightest neutron star ever observed had a mass that was 1.17 times that of the Sun.

Not only is this more recent discovery smaller, but it is also significantly smaller than the minimum mass of a neutron star that is predicted by theory. This suggests either that we don't know enough about these ultradense objects, or that what we're looking at is a strange, never-before-seen object called a "strange" star instead of a neutron star.

The densest objects in the universe are neutron stars. They are what remain after a massive star with a mass between 8 and 30 times that of the Sun has passed away. The star goes supernova, ejecting its outer layers of material into space, when it runs out of material to fuse in its core.

The core collapses in on itself, no longer supported by fusion's outward pressure, making it so dense that atomic nuclei squish together and electrons are forced to become close to protons for long enough for them to become neutrons.

The majority of these small objects are about 1.4 times as big as the Sun, but theory says they could be as small as 1.1 solar masses or as big as 2.3 solar masses. Every teaspoonful of neutron star material weighs between 10 million and several billion tons because all of this is contained within a sphere that is just 20 kilometers (12 miles) across.

Even stars with masses that are higher or lower than neutron stars can become dense. Black holes form when heavier stars collide. White dwarfs form from lighter stars. They are less dense than neutron stars and have a mass limit of 1.4 solar masses, but they are still pretty compact. This will eventually happen to our Sun.

This study's neutron star is at the center of a supernova remnant known as HESS J1731-347, which was previously estimated to be more than 10,000 light-years away. Poorly constrained distance measurements, on the other hand, present one of the challenges in the study of neutron stars.It is difficult to measure a star's other characteristics accurately without knowing its precise distance.

In HESS J1731-347, a second, optically bright star was recently discovered. A group of astronomers led by Victor Doroshenko of Eberhard Karls University of Tübingen in Germany was able to recalculate the distance to HESS J1731-347 using data from the Gaia mapping survey. They discovered that the object is much closer than previously thought, at approximately 8,150 light-years away.

This indicates that previous estimations of the neutron star's other characteristics, such as its mass, needed to be improved .Doroshenko and his colleagues were able to reduce the neutron star's mass to an astonishingly low 0.77 solar masses by combining it with observations of the neutron star's X-ray light, which was inconsistent with X-radiation from a white dwarf.

This indicates that it may not be a neutron star as we know it, but rather a hypothetical object that has not yet been positively identified in the real world.

According to the authors of the paper, "Our mass estimate makes the central compact object in HESS J1731-347 the lightest neutron star known to date, and potentially a more exotic object – that is, a candidate for a "strange star"."

Theoretically, a strange star is similar to a neutron star in appearance, but it contains more strange quarks, fundamental particles. Protons and neutrons are composite particles made of quarks, fundamental subatomic particles. There are six distinct flavors—up, down, charm, strange, top, and bottom—of quarks. Up and down quarks make up protons and neutrons.

Subatomic particles are thought to be broken down into their constituent quarks in a neutron star's extremely compressed environment, according to theory. According to this model, strange stars are made of matter with up, down, and strange quarks in equal amounts.

The rulebook for neutron stars breaks when enough quarks are involved, so there is essentially no lower limit either. Strange stars should form at masses large enough to really put the squeeze on.This means that the possibility of this neutron star actually being a strange star cannot be ruled out.

This would be fantastic; For a number of decades, physicists have been looking for quark matter and strange quark matter. However, while a strange star is definitely possible, the more likely scenario is a neutron star, which is also incredibly cool.

"The obtained constraints on mass and radius can be used to improve astrophysical constraints on the equation of state of cold dense matter under this assumption," the researchers write. "The obtained constraints on mass and radius are still fully consistent with a standard neutron star interpretation."

"Such a light neutron star appears to be a very intriguing object from an astrophysical perspective, regardless of the assumed internal composition."

Under our current models, it is difficult to determine how such a light neutron star could have formed. The dense object at the center of HESS J1731-347 will, therefore, have something to teach us about the enigmatic afterlives of massive stars, regardless of its material composition.

The team's research has been published in Nature Astronomy.