Scientists Discover Incredibly Large, Unusual Star Twice as Massive as Sun

Every year, scientists spot a dozen or two new examples of what they call galactic millisecond pulsars—the incredibly dense corpses of stars that spin hundreds or even a thousand times a second.

But even among these extraordinary stars, there are some that stand out. Like one known as PSR J2215+5135, which scientists describe in a recent paper published in The Astrophysical Journal.

PSR J2215+5135 is actually a pair of stars, spinning around each other every four hours in a mess that makes it difficult for scientists to study either one alone. One of the stars is a perfectly normal, boring star about a third the size of our sun, but the other is something truly incredible—not only is it one of these millisecond pulsars, but it is absolutely huge.

Read more: New NASA Space Telescope Photo Reveals Thousands of Stars, and Maybe Planets Too

The pulsar contains more than double the mass of our sun—which might not sound very impressive on its own. But sun-like stars and neutron stars, the general term for super-dense stellar corpses formed by explosions regardless of how quickly they spin, stack up very differently.

That's because those explosions are messy affairs that result in much of a star's mass being shot out into space—so a star capable of forming a neutron star twice the mass of the sun would have been very large indeed, and such large neutron stars were rare.

In fact, scientists once thought they couldn't get any larger than about one and a half times the size of the sun. PSR J2215+5135 isn't the first to overturn that belief, but its size still makes it extremely rare.It may even be the very largest pulsar known to date, although the uncertainty around measuring these masses makes that difficult to say for sure.

Neutron stars produce jets of particles like those shown here, from a neutron star about 12 miles wide (not PSR J2215 5135). REUTERS/X-ray: NASA/CXC/Univ of Toronto/M.Durant et al; Optical: DSS/Davide De Martin/Handou

The new work brings together data collected at three different telescopes to look at the pair of stars in diferent ways. That said, the scientists still want to confirm their size estimates using a technique called stellar inclination, just to be sure.

But if the current calculations hold true, they write, they could have major consequences for astrophysics: "If confirmed, such a massive pulsar would rule out some of the proposed equations of state for the neutron star interior."