Category: Black Holes

Astronomers now believe there’s a supermassive black hole at the centre of almost every galaxy in the Universe. These black holes can have millions, or even hundreds of millions of times the mass of the Sun. Unlike stellar mass black holes, the supermassive versions might have formed differently, going from a cloud of gas directly to a black hole – skipping the star stage entirely.

Since their discovery, astronomers still don’t really know how supermassive black holes got going. But there they are, inside most galaxies. In fact, quasar observations show that supermassive black holes were present in the early Universe. Quasars are some of the brightest objects in the Universe, blazing from the radiation emitted by supermassive black holes actively consuming material.

One possibility is that these monsters had humble beginnings, starting out as a massive star, going supernova, and then becoming a black hole. It’s a process astronomers understand fairly well. The problem with this theory is that these early supermassive black holes must have been growing constantly right from the beginning, at the maximum rate predicted by physics. And as we see today, galaxies go through active and quiescent stages depending on when their black hole is consuming material.

But a second possibility is that these black holes formed directly, pulling together so much material that they bypassed the stellar stage entirely.

Dr. Mitchell C. Begelman, a professor in the Department of Astrophysical and Planetary Sciences at the University of Colorado, Boulder recently published a paper entitled Did supermassive black holes form by direct collapse? This paper sketches out this alternate theory of black hole formation in the early Universe.

After the Big Bang, the Universe cooled enough for the first stars to form out of the original hydrogen and helium. This was pure material, unpolluted by previous generations of stars. Astronomers have calculated that these first stars, called Population III, would have a maximum rate that they could gather material together to form a star.

But what if there was much more gas around? Way beyond the limits that could form a star.

With a regular star, material comes in relatively slowly, creating a central mass. With enough mass, the star ignites, and this creates and outward pressure that stops further material from compacting too tightly.

But Dr. Begelman has calculated that if the infall rate exceeds just a few tenths of a solar mass per year, the stellar core would be so tightly bound that the energy release of nuclear fusion wouldn’t be enough to stop the core from continuing to contract. You would never have a star, you would just go from a cloud of hydrogen to a tightly bound central mass. And then a black hole.

The question is, would it be possible to have material come together so quickly? It can, if something’s pushing it… like dark matter. According to Dr. Begelman, there could be several situations where an external force, like the gravity from a large halo of dark matter which could work to force gas into a central area. In fact, material has been calculated falling into a black hole this quickly, because that’s the rate it takes to power quasars. But the question is, will this work if the black hole isn’t there, or really small.

Once there are a few solar masses of accumulated gas, the core begins to shrink under the pull of its increasing mass. The object goes through a brief period of nuclear fusion when it reaches 100 solar masses, but it passes through this phase so rapidly that it doesn’t get a chance to expand again.

Eventually the object reaches several thousand solar masses, and its temperature has climbed to several hundred million degrees. At this point, gravity finally takes over, collapsing the core, and turning the object into a 10-20 solar mass black hole which then starts consuming all the mass around it.

From this point on, the black hole is able to draw in further material efficiently, growing at the maximum levels predicted by physics, eventually gathering up millions of times the mass of the Sun. If too much material falls in, the baby supermassive black hole might act like a mini-quasar – Dr. Begelman has dubbed this a “quasistar” – blazing with radiation as infalling material backs up in the black hole’s surroundings.

And there’s the good news: these quasistars might be detectable by powerful telescopes. However, they would have very short lifetimes, only lasting 100,000 years. They might be marginally detectable by the upcoming James Webb Space Telescope.

Original Source: Arxiv paper

New observations from the Spitzer Space Telescope indicate that supermassive black holes at the heart of elliptical galaxies might keep temperatures so high that gas can’t cool down. And without large clouds of cool gas, new stars can’t form. As long as the black hole is raging, star formation in the galaxy is put on hold.

Thanks to the Spitzer observations, astronomers have detected dust grains mingling with blazing hot gas at temperatures of 10 million degrees Celsius in an area surrounding the elliptical galaxy NGC 5044. Astronomers have seen this kind of situation before, where hot gas surrounding galaxies blaze hot in the X-ray spectrum.

There are many kinds of galaxies. Spiral galaxies like our own Milky Way have active regions of star formation. The older, larger, redder elliptical galaxies are different. They’re found at the centres of galaxy clusters, and have large quantities of hot gas that never seems to cool down enough to begin star formation.

Researchers from UC Santa Cruz think that this hot gas is being heated by the supermassive black holes through a process called feedback heating. They believe that material ejected by dying stars gravitates towards the centre of the galaxy. As it approaches the black hole, a large amount of energy is released, heating the gas up. This makes it buoyant, sort of like how smoke and embers float away from a fire. These plumes then mix with other, more distant gas, and heat it up as well. Each time the supermassive black hole feeds, it creates a feedback effect that travels outward, heating up gas across the galaxy.

And this is what kills star formation. Stars can only form when dust is cool enough to condense together, like water makes steam – you only get rain when it cools down. With all this heated gas, material never comes together to create stars.

Original Source: Spitzer News Release

There’s a book by Larry Niven called “Hole Man”, where a group of explorers on Mars come across an alien communications device. One of the scientists thinks there’s a microscopic black hole inside, which powers the device, and to prove it, he turns off the containment field. The black hole falls into Mars, consuming the planet from within, and threatening the entire solar system.

Just science fiction? Maybe not. According to B.E. Zhilyaev, a researcher at the Main Astronomical Observatory in Ukraine, in the research paper Singular Sources of Energy in Stars and Planets, the Universe could be buzzing with these microscopic blackholes. They might even be inside stars and planets.

This isn’t a new concept. Physicists have been theorizing about the possibility of microscopic, primordial black holes for years, and used them to explain everything from dark matter to gamma ray bursts.

It takes a star several times the mass of our Sun to form a black hole naturally when it dies, so there probably isn’t a process that can make them any more. But during the first few moments after the Big Bang, the entire Universe was compressed into a microscopic singularity. These primordial black holes could have been generated right at the beginning, and have been with us ever since.

It’s also theorized that the new Large Hadron Collider might be capable of creating microscopic black holes through the collision of particles at relativistic velocities.

Before you can wrap your head around this research, consider how big a black hole has to be. For a stellar mass black hole, the event horizon – the point at which nothing can escape – is only a few kilometres from its centre. A black hole with the mass of the Earth? It would be less than 2 cm across. A black hole with the mass of a mountain? Smaller than a hydrogen atom.

Even though a microscopic black hole might contain the mass of a mountain, it would experience almost no friction as it passed through regular matter. It would fall through regular material as if it wasn’t there.

In most encounters with stars, these black holes would pass right through. But in a three-body interaction, between a star and a planet for example, the black hole could be trapped inside the star. The black hole would then orbit inside the star for billions of years until it comes to rest at the centre. They could form with the stars and planets from a protostellar cloud of gas and dust, or be captured and incorporated later.

So how do you know if you’ve got a black hole in your star? As the black hole grows over time, it starts to change the amount of heat generated by the star. A large enough black hole could cause the star to expand in size, and even undergo a supernova prematurely. According to Zhilyaev the interactions between stars and microscopic black holes could be detectable through bursts of gamma rays.

And if a black hole gets inside your planet? You get additional heat. This might account for unusual temperatures seen on Saturn and Jupiter, which are hotter than they should be from solar heating alone. A black hole inside the Earth might actually raise temperatures on the surface enough to sustain animal life long after the Sun dies out.

A power source that would last for eons, providing the most efficient possible conversion of matter to energy. Just don’t think about the monster consuming the ground beneath your feet as it keeps you warm.

Galaxies get bigger and bigger through galactic mergers. Two small galaxies come together, merge their stars, and you get a bigger galaxy. But astronomers have always wondered, what happens with the two supermassive black holes that seem to always lurk at the heart of galaxies. What happens when two compact objects with millions of times the mass of our sun collide? Good question.

An international team of physicists have developed a computer simulation designed to answer this very question. And in a recent article in Science Express, they published the results of the simulation.

It turns out the interaction depends a lot on the amount of hot gas surrounding each black hole. As they start to interact, this gas exerts a frictional force on the black holes, slowing down their spin rate. Once they get within the width of our solar system, they should start emitting gravitational waves, which continues to extract energy from the system. This causes them to continue coming together, and eventually merge.

This simulation is good news for experiments designed to search for gravitational waves. The mergers should be so energetic, they’ll generate gravitational waves detectable across space.

Original Source: Stanford News Release

An international team of astronomers have discovered a supermassive black hole at the very edge of the observable Universe, located 13 billion light-years away. Since the Universe is 13.7 billion years old, we’re seeing this object when the Universe was only 700 million years old. Wow.

Active galactic nuclei, or quasars, occur when a supermassive black hole is feasting on infalling material. Material piles up faster than the black hole can feed, and it starts to glow so brightly that astronomers can see it clear across the Universe. This object, CFHQS J2329-0301, was discovered as part of a new distant quasar survey performed with the MegaCam imager on the Canada-France-Hawaii Telescope (CFHT).

The black hole powering the quasar is thought to have 500 million times the mass of the Sun – that makes it hungry and bright. And because the quasar is so bright, astronomers can use it as a background object to examine the gas in front. And with follow up observations, they can get more details about what kind of galaxy it formed inside.

Original Source: Canada-France-Hawaii Telescope News Release