With a mass about three-quarters our Sun crammed into a sphere that could comfortably sit in Manhattan, the compact XMMU J173203.3-344518 object is certainly notable. Strange even. Maybe bizarre.
But is it weird? A new study by astrophysicists at the University of São Paulo and the Federal University of ABC in Brazil confirms that this overwhelmingly dense clump of stellar material may indeed be strange, but perhaps not in the way you might think.
Last yearresearchers at the Institute for Astronomy and Astrophysics at the University of Tübingen in Germany have recalculated the distance between us and the tiny corpse of a dead star spinning away inside the supernova remnant HESS J1731-347.
At a distance of just 8,150 light-years, the revised proximity fell short of the previous estimate of about 10,000 light-years. The new distance required a recalculation of the compact object’s properties, particularly its size and mass.
This is where things got a little exciting.
When stars of a certain mass run out of fuel from which their gravity can conveniently snuff out daylight, they collapse in a cosmic thunderbolt of heat and electromagnetism that blows away part of their outer envelope.
All that’s left is an object so dense that its atoms are crushed cheek to cheek. Deep in its core, electrons are stuck in their nuclei, forcing protons to lose their charge and convert into neutrons. Congratulations, it’s a newborn neutron star.
Given enough mass, all that extra gravity overcomes critical nuclear forces to shred matter into something unimaginable and create one black hole instead of this. Too little mass, and atoms remain friendly neighbors in what is known a white dwarf.
This lower mass limit for a neutron star is believed to be just over one solar mass. The easiest recognized so far only 1.17 times the mass of the sun.
With 77 percent of a solar mass, XMMU J173203.3-344518 is not only record-breaking; it’s downright confusing. Neutron stars have nothing to do with being so dainty.
Which implies that it might not be a neutron star at all. Instead, an object called a was speculated strange star — composed mostly of particles known as weird quarks — the researchers left their conclusions to other researchers to play around with.
This new investigation picked up where that last study left off, returning to the unusually small, compact object in HESS J1731-347 and checking its mass, radius and surface temperature.
Comparing their results to odd matter equations and speculative models for their formation in supernovae, the team agreed that this odd little object still has all the hallmarks of a hypothetical odd star.
Quarks are elementary particles that group in trios to form baryons. Two of the better known examples of these groups are the nuclear particles protons and neutrons.
Focus enough energy on one point, and these bundles of quark goodness can overcome the forces binding them to arrange themselves into something less structured. Pressurize this hot soup enough, and its quarks might present themselves as a new form of matter, unsurprisingly called quark matter.
Quarks come in a variety of shapes or flavors. “Up” and “Down” flavors mix and match to form protons and neutrons. With enough pressure, down quarks can transform into up quarks, which in turn can change into another flavor – a strange quark.
How a supercompact object composed mostly of strange quarks emerges from a supernova is not yet clear, although some models suggest that quark matter typically evolved early in the collapse.
Under rather unique conditions, something causes this matter to dominate and release even more energy when it collapses to shed more mass than usual, leaving this excess of quarks behind.
Coming back to the most recent study, their revised estimates of the age and surface temperature of XMMU J173203.3-344518, as well as the object’s radius and tiny mass, agree with the cooling conditions that point to its strange composition.
That doesn’t mean something more “normal” can be ruled out. It gives the astronomical community even more reason to point their telescopes at XMMU J173203.3-344518 as it is a landmark case.
As the authors argue“It is premature to draw a stronger conclusion, although this is an important case and other discoveries may complete the picture.”
This research was adopted in Astronomy and Astrophysics Letters and is currently available on arXiv.
