Posted on 01/19/2018 1:38:43 PM PST by Red Badger
These remaining cores of dead stars can only get so massive before they become black holes.
_______________________________________________________________________________________________________________________________________
The subtle difference between when a massive dying star compresses into a core and when it collapses entirely may have been found. In a study published in Astrophysical Journal Letters, researchers at the Goethe University in Frankfurt say they’ve found the dividing line between compact objects called neutron stars and black holes.
When a massive star reaches the end of its life, it goes out with an immense bang called a supernova. From there, one of two known things Can happen: it either becomes a black hole, which has so much gravity not even light can escape, or a neutron star, which is a city-sized corpse of a formerly large star that’s made out of incredibly dense neutron matter.
But astrophysicists have struggled to find out exactly what variations cause a large star to compress into a dense stellar remnant, a neutron star, rather than the inescapable void of matter-eating fury that is a black hole. According to the Goethe researchers, the difference is simple: 2.16 solar masses. Any leftover object after a supernova that is less than 2.16 times the mass of the sun will start a neutron star, while anything more than 2.16 solar masses will become a black hole.
Most neutron stars are between one and two solar masses, and most black holes discovered so far (or at least suspected so far, since we can’t directly see something that gives off no light) are four solar masses or above.
So why is this important? Researchers are still studying the results of a new phenomena witnessed last year called a kilonova. It created ripples in the fabric of space-time that were detected from Earth. While it was widely reported to be a merger of two neutron stars, some researchers aren't sure if the larger object was in fact one of these dense stellar cores. The larger object was estimated to be between 1.36 and 2.26 solar masses, while the smaller was well within the mass range of an average neutron star.
If it is toward the upper end of that mass estimate, then we may have witnessed the merger of a black hole and a neutron star—which could be essential to the research taking place in the wake of the explosion, as astronomers delve deeper into what kind of object is left behind at the center of such an event. A large, unstable neutron star that swiftly became a black hole could have been left behind after the kilonova, if it was a merger of two neutron stars, or an entirely different event could have taken place where a black hole ingested the smaller neutron star. The latter type of event has been identified before, at least tentatively, in 2005.
The Goethe researchers suggest that adding even a little more mass to the object could cause it to collapse into a black hole—however, some researchers have theorized, but never proven, that another type of object exists between the mass of a neutron star and that of a black hole. But with an upper ceiling to neutron star mass determined, we can begin to figure out how a large star truly dies—and what it takes to make a star fully collapse into a light-eating inferno.
Definitely not your friend. If you dropped an object 3 feet away from the surface of a neutron star, it would be going several million miles/hour when it hit the surface. That’s some pretty gnarly gravitational acceleration. If you went there, you and your spaceship would wind up as a thin film on the surface of the neutron star. That thin film would most likely be a thin smear of various subatomic particles. It would not be possible to put Humpty Dumpty back together again.
What I took from this article is that black holes are actually alien starship bases.
Good post. I was immediately wondering the same thing. This whole article makes this sound like something new.
A star maintains equilibrium by balancing two things: the pressure of the superheated gas/plasma in the star undergoing a fusion reaction acting out away from the center and gravity acting toward the center. When a star runs out of hydrogen to fuse into helium, does the fusion reaction stop and the star collapses? No. The star shrinks due to the gravity and the lack of a fusion reaction taking place, the helium is compressed harder, and pressure & temperature goes up until the helium starts fusing into a heavier element. Other than the temperature and pressure required, it undergoes a fusion reaction that gives off lots of energy. When the helium runs out, the star once again shrinks in on itself until the heavier element starts a fusion reaction again. This should theoretically go on forever, right? No. The problem is that when you reach iron in the core, the fusion reaction for that element absorbs energy instead of giving it off. Iron in the core kills your star.
What happens then? You’ve got gravity acting in and nothing appreciable pushing out anymore. At that point, your star collapses at a relativistic speed, approx. 1/3 the speed of light. If your star is 1.4 times the mass of our sun or larger, it collapses into a super-tight mass under tremendous pressure. The star under tremendous pressure rebounds in a supernova explosion that, for a short time, glows brighter than the sum-total of every other star in the galaxy (we’ve spotted supernova explosions from millions of light years away, far outside the milky way). That relativistic collapse and the material that is blown off in the explosion is where we get our heavy elements such as gold, uranium, lead, and other heavy stuff. The material that is retained by the tremendous gravity is incredibly dense and forms your neutron star or black hole depending on the mass of your original star. Our sun does this with more of a whimper and will be a white dwarf. 1.4-3.3 solar masses will get you a supernova explosion and form a neutron star. 3.3 solar masses or larger gets you a black hole.
Now to your question:
Gravity is based on the mass but also on the density. Think of the mass of the milky way: 200+ billion times our sun but it’s not a mondo super black hole because it’s so spread out. You gotta crunch mass down to get a neutron star or black hole. When your star forms iron in the core and collapses at 1/3 the speed of light, that’s where you get that big crunch and those super high densities. It doesn’t gain mass, in fact it loses mass because it ejects heavy elements. But what it does gain is DENSITY.
This is probably a grade-school question, but why did you refer to 1/3 the speed of light as a “relativistic” speed.
I presume it refers to the theory of relativity, but am not sure exactly how.
I saw similar stories about whether black holes existed
“I saw similar stories about whether black holes existed”
Yeah, they are out there. I person is not a Luddite for bringing this up.
Thanks Red Badger, and btw, I stole Salamander's graphic.
A “relativistic” speed is a significant fraction of the speed of light where weird things like time dilation and length contraction happen.
Thanks.
The density does allow you to get closer to the center of the mass, where the gravitational field wold be stronger, but since we are talking about stars and black holes, we can assume the same distance from each. The gravity of an exploding star would not change, other than to diminish due to escaping mass.
Wow, what a coincidence! Me and my buddies were discussing the mass limit for neutron stars just this past Friday night in the bar after bowling.......
And your conclusion consensus was?............................
We almost had it solved until the wife on one of the guys came in looking for him and spotted him hitting on the waitress. Then all hell broke loose.........we lost our train of thought.
This is called the Tolman–Oppenheimer–Volkoff limit, named after the three physicists who first calculated it in the 1930s. They came up with a value between 1.5 and 3 solar masses.
In 2007 a pular with 2.01 solar masses was found, which set a new lower limit. Then some researchers in 2017 set a new upper limit of 2.17, which I think is what the article might be talking about.
https://en.m.wikipedia.org/wiki/Tolman–Oppenheimer–Volkoff_limit
This figure is for the residual mass. About 90% of the original mass gets blown into space.
So it’s about 2.1 solar masses?............
So Betelgeuse has a black hole at its center right now?
Disclaimer: Opinions posted on Free Republic are those of the individual posters and do not necessarily represent the opinion of Free Republic or its management. All materials posted herein are protected by copyright law and the exemption for fair use of copyrighted works.