Does a star gain mass in order to make a black hole?

If a black hole is the remnants of an extremely large collapsed star, how does gravity of the dead star increase to create the black hole? Light could obviously escape the gravity of the star and the black hole is made from the dead star but, once the black hole is created, light can no longer escape. Does the mass somehow increase at the death of the star?
In this artist’s portrayal of the IC 10 X-1 system, the black hole lies at the upper left and its companion star is on the right. The two objects orbit around a center of gravity once every 34.4 hours. The stellar companion is a type known as a Wolf-Rayet star. Such stars are highly evolved and destined to explode as supernovae. The black hole companion is shedding its outer envelope in a powerful wind, and some of this gas is captured by the black hole’s powerful gravity. redit: Aurore Simonnet/Sonoma State University/NASA.

In this artist’s portrayal of the IC 10 X-1 system, the black hole lies at the upper left and its companion star is on the right. The two objects orbit around a center of gravity once every 34.4 hours. The stellar companion is a type known as a Wolf-Rayet star. Such stars are highly evolved and destined to explode as supernovae. The black hole companion is shedding its outer envelope in a powerful wind, and some of this gas is captured by the black hole’s powerful gravity. redit: Aurore Simonnet/Sonoma State University/NASA.

Originally posted at Forbes! 

Your standard black hole is indeed the remnants of an extremely large, collapsed star, with the remnant sitting somewhere between 5-20 times more massive than our own sun. However, if we let nature produce a black hole, the black hole that is produced at the end of a supernova explosion is actually significantly less massive than the star that it once was.

The Hubble Space Telescope imaged this view in February 1995. The arcing, graceful structure is actually a bow shock about half a light-year across, created from the wind from the star L.L. Orionis colliding with the Orion Nebula flow. Image Credit: NASA

The Hubble Space Telescope imaged this view in February 1995. The arcing, graceful structure is actually a bow shock about half a light-year across, created from the wind from the star L.L. Orionis colliding with the Orion Nebula flow. Image Credit: NASA

Part of the drop in mass between star and black hole comes in the years before the supernova, when the star typically sheds a sizable fraction of its mass. Since the star has expanded so much as part of the red giant phase, it only has a loose gravitational grasp on the outer layers of its atmosphere, and they are easily pushed away from the star by the star’s stellar wind. Our sun has a stellar wind as well, and it’s one of the reasons Mars is still losing its atmosphere to space - it’s also the reason Earth’s magnetosphere is such a nice feature of our planet; we’re protected from this kind of atmospheric blasting by the sun. However, the Sun’s stellar wind is dragging many fewer particles along with it, compared to a red giant star, so the sun’s mass loss is much less than it would be if it were a red giant.

The star has pre-emptively lost some of the mass it contained before it became a red giant, but there’s also the supernova explosion itself to consider. A good chunk of the material that was left within the star goes blasting outward, fast and hot enough to barrel into any gas and dust nearby and produce X-rays. It’s really only the very core of the star that stays put, and can be compressed into the black hole.

This composite image of a supernova remnant combines infrared and X-ray observations. The explosion left a blazing hot cloud of expanding debris (green and yellow). The location of the blast's outer shock wave can be seen as a blue sphere of ultra-energetic electrons. Newly synthesized dust in the ejected material and heated pre-existing dust from the area around the supernova radiate at infrared wavelengths of 24 microns (red). Foreground and background stars in the image are white. Image Credit: MPIA/NASA/Calar Alto Observatory.

This composite image of a supernova remnant combines infrared and X-ray observations. The explosion left a blazing hot cloud of expanding debris (green and yellow). The location of the blast's outer shock wave can be seen as a blue sphere of ultra-energetic electrons. Newly synthesized dust in the ejected material and heated pre-existing dust from the area around the supernova radiate at infrared wavelengths of 24 microns (red). Foreground and background stars in the image are white. Image Credit: MPIA/NASA/Calar Alto Observatory.

If the mass of the star is actually only partially transformed into a black hole, then I’ve actually made the paradox in your question worse. How is the gravitational pull of a much bigger star (which light can escape from) so much weaker than a black hole made of only a fraction of the star (which light can’t escape from)?

The gravitational pull from a large object on a small one, at any point in space, is only determined by the mass of the heavy object, the mass of the smaller object, and the distance between the centers of the two objects. So, by this logic, if you were a cosmic wizard and replaced the sun with a black hole of equal mass, none of these parameters have changed for the planets. The planets haven’t changed their mass, or their distance from the center of the solar system where the sun used to be, and if the sun and the black hole are the same mass, then the whole system is gravitationally identical.

Obviously, there are some cosmetic differences between the black hole and the star in this scenario, but gravitationally speaking, differences only arise when you start to get very close to the objects. At the surface of our sun, which is where light escapes from the star and streams out towards the rest of the Universe, we are still 432,700 miles (696,000 kilometres) away from the center of the sun. A black hole, on the other hand, is a much denser object, so you can get far closer to its center while still having the entire mass of the black hole to contend with. It’s this density that makes the difference between light being able to escape or not.

For our magical swap scenario, you would have to get within 1.83 miles (2.95 kilometers) of the coordinates marking the very center of the Sun (or where it used to be) before you would cross the event horizon, where light would no longer be able to escape. Within that sphere, 3.66 miles from edge to edge, is the entire mass of our current sun, packed into a single pinprick’s worth of space, instead of filling 432,700 miles of space.

It’s the same scenario with the black hole produced at the end of a supernova; the black hole hasn’t grown in mass, or expanded its gravitational reach- it’s simply much more dense, so you (or light) can get much closer to the center of the black hole, while still being pulled on by the full mass of the black hole. It’s this combination of proximity and mass concentration that produces the gravitational extremes we’ve come to associate with black holes!

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What Happens To The Material Flung Out By A Supernova?

How fast does the matter expelled by a supernova travel? Hydrogen will be the fastest, but is it going a significant fraction of the speed of light? How far does the matter travel before its sucked in by the gravity of the nearest big object or the surrounded ejected mass? Does the matter ejected from a supernova sometimes collapse back in at the center of mass?
This new version of Chandra's image of the Cassiopeia A supernova remnant has been specially processed to show with better clarity the appearance of Cas A in different bands of X-rays. This will aid astronomers in their efforts to reconstruct details of the supernova process such as the size of the star, its chemical makeup, and the explosion mechanism. The color scheme used in this image is the following: low-energy X-rays are red, medium-energy ones are green, and the highest-energy X-rays detected by Chandra are colored blue. Image Credit: NASA/CXC/SAO.

This new version of Chandra's image of the Cassiopeia A supernova remnant has been specially processed to show with better clarity the appearance of Cas A in different bands of X-rays. This will aid astronomers in their efforts to reconstruct details of the supernova process such as the size of the star, its chemical makeup, and the explosion mechanism. The color scheme used in this image is the following: low-energy X-rays are red, medium-energy ones are green, and the highest-energy X-rays detected by Chandra are colored blue. Image Credit: NASA/CXC/SAO.

Originally posted at Forbes!

What happens after a supernova occurs depends on a number of things, but hydrogen isn’t even close to the fastest thing that gets blown away from the dying star. You’re thinking along the right lines though, in that hydrogen is the lightest element, and therefore the easiest to accelerate of all of the periodic table, but when we’re dealing with supernovae, we’re not limited to just the pieces that are listed as a standalone element.

The former star is producing a huge amount of energy in a very short period of time by definition, as a supernova – with this kind of energy around, atoms are not in their neutral state as we might find them on earth. The vast majority of them will be ionized in some form, meaning that one or more of their electrons has absorbed so much energy from the surroundings that they have escaped their atom and are careening around as loose particles. Electrons with this sort of energy are moving much faster than the protons and neutrons they left behind, but even they aren’t the fastest things coming out of the supernova.

This image shows the remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the centre of the remnant. Hubble (in green) and Chandra (in blue) data show the expanding shock wave. Image credit: ALMA (ESO/NAOJ/NRAO)/A. Angelich. Visible light image: the NASA/ESA Hubble Space Telescope. X-Ray image: The NASA Chandra X-Ray Observatory

This image shows the remnant of Supernova 1987A seen in light of very different wavelengths. ALMA data (in red) shows newly formed dust in the centre of the remnant. Hubble (in green) and Chandra (in blue) data show the expanding shock wave. Image credit: ALMA (ESO/NAOJ/NRAO)/A. Angelich. Visible light image: the NASA/ESA Hubble Space Telescope. X-Ray image: The NASA Chandra X-Ray Observatory

That award goes to the neutrino, which is a super tiny fundamental particle which very rarely interacts with matter through any other force than gravity. Because its mass is so small (for a while we thought they might be entirely massless, like the photon), they can travel at speeds that are very close to the speed of light. Neutrinos are produced in our sun, and are produced in much larger quantities in supernova. Because they’re traveling so fast and interacting so rarely, we can often detect the burst of neutrinos arriving at Earth before we can spot the rise in brightness from the explosion, as we did with Supernova 1987A, pictured above. The neutrinos can escape from the core of the star quickly without interacting with the rest of the star, but the burst of light that we can observe has to wait until the explosion, which begins at the very center of the star, reaches the star’s surface. (This is not a long delay; for Supernova 1987A it was only a few hours.)

Electrons are still zipping around pretty quickly though – they’re moving fast enough to create X-rays, which can then be observed with X-ray telescopes out in space. In order to do this, they have to be moving at relativistic speeds, where talking about their speeds in terms of the fraction of the speed of light is actually a useful metric.

In commemoration of the 15th anniversary of NASA's Chandra X-ray Observatory, four newly processed images of supernova remnants dramatically illustrate Chandra's unique ability to explore high-energy processes in the cosmos (see the accompanying press release). The images of the Tycho and G292.0+1.8 supernova remnants show how Chandra can trace the expanding debris of an exploded star and the associated shock waves that rumble through interstellar space at speeds of millions of miles per hour. The images of the Crab Nebula and 3C58 show how extremely dense, rapidly rotating neutron stars produced when a massive star explodes can create clouds of high-energy particles light years across that glow brightly in X-rays. Image credit: NASA/CXC/SAO

In commemoration of the 15th anniversary of NASA's Chandra X-ray Observatory, four newly processed images of supernova remnants dramatically illustrate Chandra's unique ability to explore high-energy processes in the cosmos (see the accompanying press release). The images of the Tycho and G292.0+1.8 supernova remnants show how Chandra can trace the expanding debris of an exploded star and the associated shock waves that rumble through interstellar space at speeds of millions of miles per hour. The images of the Crab Nebula and 3C58 show how extremely dense, rapidly rotating neutron stars produced when a massive star explodes can create clouds of high-energy particles light years across that glow brightly in X-rays. Image credit: NASA/CXC/SAO

In terms of where the matter goes, what we typically see as the supernova remnant in these images is the shock front of the ejected material hitting the gas and dust which surrounded that star. As the surrounding gas and dust will be a little differently arranged for each star, the shock front will have a slightly different shape for each supernova as well. And depending on the density of the material the shock front is running into, the expansion of the shock front will continue at different speeds. Inside that edge, there can be a reverse shock, where material has raced up behind the shock front, and bounced off of it, and is reflected back towards the inside, heating up the material on the inside of the supernova bubble to very high temperatures.

The supernova explosion of a star ejects most (Type II), and in some cases all (Type Ia), of the star into space at speeds of millions of miles per hour into the circumstellar gas. This event generates shock waves that produce shells of hot gas and high-energy particles that are observed for hundreds and thousands of years as supernova remnants. (Illustration: NASA/CXC/M.Weiss)

The supernova explosion of a star ejects most (Type II), and in some cases all (Type Ia), of the star into space at speeds of millions of miles per hour into the circumstellar gas. This event generates shock waves that produce shells of hot gas and high-energy particles that are observed for hundreds and thousands of years as supernova remnants. (Illustration: NASA/CXC/M.Weiss)

 

Once the material is expelled outwards into the shock front, it’s unlikely to fall back to the center; it’s too far away and moving too fast. It’s the material closer to the stellar remnant, which wasn’t initially collected into the remnant, but also didn’t get pushed very far away, still close to the center of the supernova bubble, which has the potential to fall back down over time.
 

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