Neutron Stars Collide in New LIGO Signal?

SPEAKER_1 (0:00)

This episode is brought to you by Indeed. You're ready to level up your business, but the pressure to find the right person to make that happen is intense. Indeed Sponsored Jobs can help carry the load. It boosts your job post to help it reach quality talent fast. Cut through the chaos with Indeed Sponsored Jobs. Get a $75 sponsored job credit at indeed.com/podcast.

Terms and conditions apply.

Hiring now? Then this is a job for Indeed Sponsored Jobs.

SPEAKER_2 (0:30)

Whenever fall comes back around, it always feels like a fresh start. This year I've been layering in some styles from the new Lululemon Fall Drop because the weather is shifting and I find I have to be ready for the entire day and not just one part of it.

Lululemon's fall line has some really versatile transitional pieces so I can just wake up, throw on a matching set, add a jacket or a fleece and head out, knowing that I'll feel comfortable enough to go wherever the day takes me. Check out the new fall arrivals in store and online now at lululemon.com.

Matt O'Dowd (1:03)

This episode is brought to you by Curiosity Stream. Last year, LIGO announced the detection of gravitational waves from the merger of two black holes. The science world went a little crazy. But only a few weeks ago, a new rumor emerged that LIGO had, for the first time, spotted gravitational waves from the collision of a pair of neutron stars. If this is true, some long-standing astrophysical mysteries are about to be unlocked.

When the Laser Interferometer Gravitational Wave Observatory, LIGO, detected gravitational waves from a pair of merging black holes, an entirely new realm of the universe opened up to science.

We now have an observatory that can explore the most extreme gravitational phenomena in the universe. Check out our episodes on the LIGO detections for more info.

Since the first, LIGO has announced the detection of two more black hole mergers. As the data comes in, we're learning a ton about black holes, how they grow, and the stars that produce them. But the merger of binary black holes isn't the only game in town. LIGO was supposed to also detect some other crazy stuff, like certain types of supernova explosion and the merger of binary neutron stars. It may have just done so. Rumors are abound that LIGO has finally spotted the long-expected neutron star-neutron star merger, and that the event was accompanied by a bright flash of gamma rays. The rumor has already been hyped all over the press, so let's dissect it with a skeptical eye. But before we figure out whether the rumor is true, in fact, before we talk about the supposed signal at all, let's refresh our memory on neutron stars. When a massive star ends its life in a supernova explosion, it leaves behind an ultra-dense core. For the most massive stars, that core will collapse into a black hole, but there's an intermediate range. A remnant core between 1.4 and around 3 times the mass of our sun instead ends up as a neutron star. These insane objects carry the mass of a star within a sphere the size of a city, around 18 km in diameter. They are mostly composed of neutrons at the density of an atomic nucleus and are held up by a quantum mechanical force called degeneracy pressure. We talk about the bizarre physics of these quantum and gravitational monsters in this video. Neutron stars can rotate up to thousands of times per second and have enormous magnetic fields that result in jets of near-light speed particles that sweep through space like a lighthouse. When those jets sweep past the Earth, we see the regular flashes of a pulsar. In fact, the first real evidence of the existence of gravitational waves came from a pulsar. This was the Holtz-Taylor binary. Two neutron stars in orbit around each other, one of which is visible to us as a pulsar. This binary pair stirs up space time in its vicinity, creating ripples that travel outwards as gravitational waves. And that gravitational radiation sucks energy from the orbiting system, causing the neutron stars to spiral inwards. By monitoring the pulses of one of those stars, this in-spiral was measured. The rate of loss of orbital energy exactly matches the expected rate of emission of gravitational radiation. Any neutron stars or black holes in close orbit with each other will eventually collide as they leak gravitational radiation. We now know of plenty of neutron star pairs in binary orbits. In fact, we expect them to be much more common than black hole binaries. Why? Well, because the universe makes far more neutron stars than black holes. You see, black holes only form in the depths of the most massive stars. Those over approximately 20 times the sun's mass. But these are also the rarest of stars. Neutron stars form from the not quite as rare stars of around 8 to 20 solar masses. That means neutron stars should be more common than black holes, and neutron star binary systems should merge more often than black hole binaries. So why isn't LIGO seeing lots of them? Well, again, it's because of mass. The remnant core of a dead star must be less than 3 solar masses to make a neutron star. But that's a factor of 10 smaller than the 30 solar mass black holes that merged in the first LIGO detection.