>>Most ULX’s are long lasting. Astronomers think they are created by super-dense objects—like black holes—feeding on nearby stars. The gravity of the black hole rips the star to pieces, creating a disk of debris. The material at the inner edge of the disk accelerates to speeds so fast that it heats up to millions of degrees and begins emitting powerful X-rays.

But that doesn’t explain how the mysterious green blob winked in and out of existence so quickly. The fact that no visible light was associated with the X-ray burst suggests that it was not a supernova, which usually shine brightly. The event was possibly a black hole gobbling up a very small star, which produced the short energetic burst.

Another possibility is that the event was created by a neutron star, the core of a giant star that collapsed in on itself during a supernova. Though they are only about 12.4 miles in diameter, these stars are super dense, with one teaspoon weighing a billion tons. Neutron stars’ gravity is also about 2 billion times stronger than gravity on Earth.

These incredibly dense stars create debris fields like black holes. Typically, the strong magnetic field around a neutron star channels debris to the surface, where it produces a steady stream of X-rays as the material is heated up and obliterated. However, if a neutron star spins particularly fast, the study authors hypothesize, the magnetic field would block the material from reaching the surface.<<

https://www.smithsonianmag.com/smart-news/astronomers-puzzle-over-blob-x-rays-winked-and-out-existence-180973062/

PermeateFree said:

Another possibility is that the event was created by a neutron star, the core of a giant star that collapsed in on itself during a supernova. Though they are only about 12.4 miles in diameter, these stars are super dense, with one teaspoon weighing a billion tons. Neutron stars’ gravity is also about 2 billion times stronger than gravity on Earth.

https://www.smithsonianmag.com/smart-news/astronomers-puzzle-over-blob-x-rays-winked-and-out-existence-180973062/

Using the numbers given, and assuming the teaspoon is heaped, with a volume of 10 ml, I get a gravity of 20 billion g, but that gives a neutron star mass of only about 70,000 Earths, whereas the Internet* suggests that their typical mass is more like 700, 000 Earths, so that gives 200 billion g gravity.

I thought that the difference would be more than that, but mass reduces in proportion to 1/radius^3, whereas gravity only increases in proportion to 1/radius^2, so it all makes sense.

• in this case the Internet is https://van.physics.illinois.edu/qa/listing.php?id=1081

The Rev Dodgson said:

PermeateFree said:

Another possibility is that the event was created by a neutron star, the core of a giant star that collapsed in on itself during a supernova. Though they are only about 12.4 miles in diameter, these stars are super dense, with one teaspoon weighing a billion tons. Neutron stars’ gravity is also about 2 billion times stronger than gravity on Earth.

https://www.smithsonianmag.com/smart-news/astronomers-puzzle-over-blob-x-rays-winked-and-out-existence-180973062/

Using the numbers given, and assuming the teaspoon is heaped, with a volume of 10 ml, I get a gravity of 20 billion g, but that gives a neutron star mass of only about 70,000 Earths, whereas the Internet* suggests that their typical mass is more like 700, 000 Earths, so that gives 200 billion g gravity.

I thought that the difference would be more than that, but mass reduces in proportion to 1/radius^3, whereas gravity only increases in proportion to 1/radius^2, so it all makes sense.

• in this case the Internet is https://van.physics.illinois.edu/qa/listing.php?id=1081
  

A very slow pulsar?