Super-Neutron Stars are Possible
Written by Fraser Cain
When a star like our Sun dies, it'll end up as a white dwarf. And if a star contains 1.4 times the mass of the Sun, it'll have enough gravity to turn into a neutron star. Much bigger stars turn into black holes. But now it turns out, neutron stars can be much more massive than astronomers previously believed - and making black holes might be much more difficult.
Astronomers working with the Arecibo Observatory in Puerto Rico have increased the mass limit you need for a neutron star to turn into a black hole.
Paulo Freire, an astronomer from Arecibo presented his latest research at the Winter meeting of the American Astronomical Society, "the matter at the center of a neutron star is highly incompressible. Our new measurements of the mass of neutron stars will help nuclear physicists understand the properties of super-dense matter. It also means that to form a black hole, more mass is needed than previously thought. Thus, in our universe, black holes might be more rare and neutron stars slightly more abundant.
When these massive stars run out of fuel, they collapse down and then explode as a supernova. The core of the star is instantly compressed into a neutron star; an extreme object with a radius of roughly 10 to 16 km across and a density of billions of tonnes per cubic centimetre. A neutron star acts like a single, giant atomic nucleus.
Astronomers used to think that neutron stars needed between 1.6 and 2.5 times the mass of the Sun to collapse - any bigger and you'd get a neutron star. But the new evidence from Arecibo pushes this limit up to 2.7 times the mass of the Sun.
Although that sounds like a slight amount, it can actually have a significant impact on the ratio of neutron stars to black holes in the Universe.
In fact, scientists don't fully understand how dense neutron stars can really be, and when they might actually switch over to become black holes, "the matter at the center of neutron stars is the densest in the Universe. It is one to two orders of magnitude denser than matter in the atomic nucleus. It is so dense we don't know what it is made out of," said Freire. "For that reason, we have at present no idea of how larger or how massive neutron stars can be."
Original Source: Cornell University
Filed under: Astronomy
January 11th, 2008 at 11:42 am
"Astronomers used to think that neutron stars needed between 1.6 and 2.5 times the mass of the Sun to collapse - any bigger and you'd get a neutron star"
I think you mean a black hole at the end of this sentence, not a neutron star?
January 11th, 2008 at 12:30 pm
In theoretical calculation, the upper bound for the neutron star is around 3.2 solar mass. Anything bigger than that will become black hole.
January 11th, 2008 at 5:43 pm
One thing that puzzles me is what happens to neutron stars with Schwarzchild radius approximately the same as the radius of the star itself?
January 11th, 2008 at 9:50 pm
Well, by definition anything with a Schwarzchild radius equal to or larger than its own radius collapses into a singularity and becomes a black hole.
January 12th, 2008 at 4:00 am
I thought the Chandrasekhar limit gave 1.4 solar mass as the upper limit for white dwarfs after exhausting their nuclear fuel. As of to day there exists no specific limits for neutron stars and black holes.
January 12th, 2008 at 9:25 am
"the matter at the center of neutron stars is the densest in the Universe. It is one to two orders of magnitude denser than matter in the atomic nucleus. It is so dense we don't know what it is made out of," said Freire.
If the matter of the neutron star is densest in the universe then in comparision where does the density of the matter of a black hole lies.
January 12th, 2008 at 10:08 am
Himanshu asked:
"If the matter of the neutron star is densest in the universe then in comparision where does the density of the matter of a black hole lies."
I believe the implication here is that the mass of a black hole no longer consists of matter as we normally understand it. Perhaps someone better informed on the matter can confirm and/or clarify.
January 12th, 2008 at 12:14 pm
Ignoring how we would get it here, could a piece of neutron star matter exist on earth? Could some be created here?
January 12th, 2008 at 2:03 pm
I would have thought that the density of the matter in a black hole would have to be pretty high isn't it supposed to be a collapsed neutron star and have an intense gravitational pull that even pulls in light and therefore must surely be more dense than a neutron star? Even if all the energy is broken up into some kind of smaller parts. But then I've never been one from believing the whole little mini universes at every point in the universe so maybe that's why the black hole isn't classed as being dense?
January 13th, 2008 at 3:04 am
An earlier Paulo Freire spoke and wrote of bread and bricks and the basic dreams of man. This Paulo Freire speaks and writes of other things and quite different basic dreams of man.
Good research, good report, and good enquiry.
January 14th, 2008 at 6:32 am
"Ignoring how we would get it here, could a piece of neutron star matter exist on earth? Could some be created here?"
The neutron star material is held together by its own gravity. If you were to try and cut off a piece of it and transport it away from the neutron star, it would expand as it left the strong gravitational field.
"I would have thought that the density of the matter in a black hole would have to be pretty high"
The density of matter in a black hole is infinite, because the matter is compressed into a singularity, i.e., a point with zero dimension. This is unless and until we discover some reason why it wouldn't become a singularity when relativity and quantum mechanics are merged. However the density would still be many orders of magnitude higher than that of a neutron star.
January 22nd, 2008 at 11:49 am
is it possible that there could be a kind of "black hole star" that puts out light, but its gravitational pull is so strong that it would pull in its own light? Or is this what a black hole is?
February 11th, 2008 at 4:19 am
I was going to say that once anything crosses the event horizon, it's only direction can be down towards the singularity. I don't necessarily straight down. To stay just outside the event horizon, something would have to be orbiting at the speed of light (in a vacuum). Since something can't travel faster than the speed of light, it can't orbit inside the event horizon. I suppose it can sort of spiral down but as it gets closer it would spiral in faster. Then I wondered if something were heading almost straight in towards the singularity if it could gain enough energy to overshoot a bit and oscillate back and forth until it finally merged with the singularity. To put it another way, could the spiral "orbit" be elliptical instead of circular and would that mean the something could at some points inside the event horizon actually gain altitude over the singularity? My feeling is no, but I wonder if this could be answered in a questions podcast by Fraser and Pamela.