Pulsars are rotating neutron stars. Most neutron stars discovered today are in the form of radio pulsars. They are called radio pulsars because they emit radio waves. We can simply connect a radio telescope to a loud speaker and hear a pulsar. Pulsars sound like someone persistently knocking. Click here and listen to a slow knocking pulsar. Click here and listen to a fast knocking pulsar. So in short, we can hear a pulsar knock.
The Quran describes a star by "The one who knocks":
[Quran 86.1-3] And the heaven and the "Knocker" (Tarek in Arabic طارق) How could you know about the "Knocker"? The piercing star (Thakeb in Arabic).
The Arabic word "Thukb ثقب" means a hole; "Thakeb ثَّاقِبُ" means the one who makes the hole. The Quran is describing a knocking star that makes a hole.
Pulsars are rotating neutron stars. As more matter falls into a neutron star its mass increases and as its mass increases its gravity increases. But gravity is actually curvature of spacetime. A neutron star distorts spacetime. As more matter falls into a neutron star its distortion increases. A point will be reached where distortion would have grown so much that it makes a hole in spacetime.
How could an illiterate man who lived 1400 years ago have known that pulsars make holes in spacetime?
(Our sun is a very small star. Actually our solar system (including the atoms that you are made of) came from a dying star 100 times more massive than our sun. Some stars are even bigger than our solar system, so you can imagine how large stars are. However according to the Bible these stars are so small that they could fall on Earth: In Mark 13:24-30 Jesus said that stars will fall on Earth before his second coming. Actually he said that stars will fall on Earth before even that generation passes away. However that generation passed away a long time ago and no star ever fell on Earth nor ever will. Do you know why? Because Earth will vaporize before it even contacts a star. So the events prophesied in the Bible are supposed to occur on Earth when Earth is already vaporized!)