Science & Technology

Scientists Have Discovered the Most Massive Neutron Star Yet

Scientists have discovered a neutron star called J0740+6620 that's so massive, it teeters on the edge of collapsing into itself. In fact, J0740+6620 is the most massive neutron star ever found. This raises a lot of questions about just how the interiors of these strange stars work.

Under Pressure

So just how strange is this newly found star? J0740+6620 has a mass that's about double that of our sun, which, in cosmic terms, is relatively small. What makes it so weird is its size: It's only about 15 miles (24 kilometers) across — about as wide as the city of Chicago. This thing is extremely dense. (Scientists accurately measured J0740+6620's mass by looking at the orbit of a small star companion, called a white dwarf.)

The study, which was published in Nature Astronomy, was led by Thankful Cromartie, a Ph.D. student at the University of Virginia and the National Radio Astronomy Observatory. It reports that astronomers stumbled across J0740+6620, which is about 4,600 light-years from Earth, while searching for gravitational waves. These are ripples in space and time that happen when very massive objects interact with each other, such as when two black holes collide.

So how did scientists find such a small object via huge ripples? The key is J0740+6620's peculiar flavor of neutron star. J0740+6620 is a pulsar, which is a rapidly rotating star that emits radio waves from its magnetic poles. You can imagine pulsars as lighthouses in space that blink very, very quickly. In fact, J0740+6620 makes hundreds of rotations every second, so that's quite a speedy blink rate.

Scientists like to use pulsars to help sense gravitational waves because pulsars rotate very regularly. If there's any disturbance in the rotation, it could indicate a massive gravitational wave event happening somewhere nearby. This time around, the scientists didn't announce any new gravitational wave events — but they did get an interesting star that will reward more examination in follow-up studies.

Computer illustration showing a new pulsar just a fraction of a second after it was formed from the merger of two neutron stars. A disc of material is seen around the star, a remnant from the merging process. Eventually it will clear. A jet is seen emanating from the neutron star's magnetic poles.

Mysteries of the Deep

Scientists describe neutron stars as exotic, because it's hard to say what they're made of. We don't have a good understanding of their matter, or the "stuff" that makes up their insides.

"While astronomers and physicists have studied these objects for decades, many mysteries remain about the nature of their interiors," said West Virginia University in a statement. In its statement, the university posed a series of possibilities about what this star could show us about tiny particles of matter, including neutrons.

For example, the interior of J0740+6620 could have crushed the neutrons enough to make them a "superfluid," allowing these particles to flow freely. Alternatively, maybe the immense gravitational pressure broke down the neutrons into even smaller particles, such as quarks. And there's also the overriding question of when, exactly, the gravity of a neutron star becomes so great that it collapses and creates a black hole from which nothing — not even light — can escape.

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Read about the first discovery of gravitational waves (it wasn't that long ago!) in "Black Hole Blues and Other Songs from Outer Space" by theoretical physicist Janna Levin. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Elizabeth Howell September 18, 2019

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