Black Holes Archives

November 20, 2013December 23, 2015 by Nancy Atkinson

Best Evidence Yet for a High-Energy Jet Emanating from the Milky Way’s Black Hole

A composite image in X-ray and radio showing a likely candidate for a jet emanating from the supermassive black hole at the center of the Milky Way. X-ray: NASA/CXC/UCLA/Z.Li et al; Radio: NRAO/VLA

Jets of high energy particles emanating from a black hole have been detected plenty of times before, but in other galaxies, that is — not from the supermassive black hole at the center of the Milky Way, known as Sagittarius A* (Sgr A*). Previous studies and other evidence suggested that perhaps there were jets – or ghosts of past jets – but many findings and studies often contradicted each other, and none were considered definitive.

Now, astronomers using Chandra X-ray Observatory and the Very Large Array (VLA) radio telescope have found strong evidence Sgr A* is producing a jet of high-energy particles.

“For decades astronomers have looked for a jet associated with the Milky Way’s black hole. Our new observations make the strongest case yet for such a jet,” said Zhiyuan Li of Nanjing University in China, lead author of a study in The Astrophysical Journal.

The supermassive black hole at the center of the Milky Way is about four million times more massive than our Sun and lies about 26,000 light-years from Earth.

While the common notion is that black holes inhale and ingest everything that comes their way, that’s not always true. Sometimes they reject small portions of incoming mass, pushing it away in the form of a powerful jet, and many times a pair of jets. These jets also feed the surroundings, releasing both mass and energy and likely play important roles in regulating the rate of formation of new stars.

Sgr A* is presently known to be consuming very little material, and so the jet is weak, making it difficult to detect. Astronomers don’t see another jet “shooting” in the opposite direction but that may be because of gas or dust blocking the line of sight from Earth or a lack of material to fuel the jet. Or there may be just a single jet.

“We were very eager to find a jet from Sgr A* because it tells us the direction of the black hole’s spin axis. This gives us important clues about the growth history of the black hole,” said Mark Morris of the University of California at Los Angeles, a co-author of the study.

The study shows the spin axis of Sgr A* is pointing in one direction, parallel to the rotation axis of the Milky Way, which indicates to astronomers that gas and dust have migrated steadily into Sgr A* over the past 10 billion years. If the Milky Way had collided with large galaxies in the recent past and their central black holes had merged with Sgr A*, the jet could point in any direction.

The jet appears to be running into gas near Sgr A*, producing X-rays detected by Chandra and radio emission observed by the VLA. The two key pieces of evidence for the jet are a straight line of X-ray emitting gas that points toward Sgr A* and a shock front — similar to a sonic boom — seen in radio data, where the jet appears to be striking the gas. Additionally, the energy signature, or spectrum, in X-rays of Sgr A* resembles that of jets coming from supermassive black holes in other galaxies.

The Chandra observations in this study were taken between September 1999 and March 2011, with a total exposure of about 17 days.

Source: Chandra

November 13, 2013December 23, 2015 by Tammy Plotner

Delving Into The Mystery Of Black Hole Jets

Black hole with disc and jets visualization courtesy of ESA

The concept of a black hole jet isn’t a new one, but we still have a lot to learn about the mixture of particles found in the vicinity of them. Through the use of ESA’s XMM-Newton Observatory, astronomers have been taking a look at a black hole in our galaxy and found some surprising results.

As we know, stellar mass black holes take on materials from nearby stars. Matter from these companion stars is pulled away from the parent body toward the black hole and radiates a temperture so intense that it emits X-rays. However, a black hole doesn’t always ingest everything that comes its way. Sometimes they reject small portions of this incoming mass, pushing it away in the form of a set of powerful jets. These jets also feed the surroundings, releasing both mass and energy… robbing the black hole of fuel.

Through the study of jet composition, researchers are able to better determine what gets taken into a black hole and what doesn’t. Through observations taken at the radio wavelength of the electromagnetic spectrum, we have seen electrons crusing along at nearly the speed of light. However, it hasn’t been clearly determined whether the negative charge of the electrons is complemented by their anti-particles, positrons, or rather by heavier positively-charged particles in the jets, like protons or atomic nuclei.” With XMM-Newton’s power behind them, astronomers have had the opportunity to examine a black hole binary system called 4U1630–47 – a candidate known to have unexpected outbursts of X-rays for segments of time which last between months and years.

“In our observations, we found signs of highly ionised nuclei of two heavy elements, iron and nickel,” says María Díaz Trigo of the European Southern Observatory in Munich, Germany, lead author of the paper published in the journal Nature. “The discovery came as a surprise – and a good one, since it shows beyond doubt that the composition of black hole jets is much richer than just electrons.”

During September 2012, a team of astronomers headed up by Dr. Díaz Trigo and collaborators, observed 4U1630–47 with XMM-Newton. They also backed up their observations with near-simultaneous radio observations taken from the Australia Telescope Compact Array. Even though the studies were done close to each other – within just a couple of weeks – the results couldn’t have been more different.

According to Trigo’s team, the initial set of observations picked up X-ray signatures from the accretion disc, but there was no activity in the radio band. This is an indicator that the jets weren’t active at that time. However, in the second set of observations, there was activity in both X-ray and radio… the jets had turned back on! While examining the X-ray data from the second set, they also found iron nuclei in motion. These particles were moving both toward and away from XMM-Newton – proof the ions were part of twin jets aimed in opposite directions. However, that’s not all. There was also evidence of nickel nuclei pointing toward the observatory.

“From these ‘fingerprints’ of iron and nickel, we could show that the speed of the jet is very high, about two-thirds of the speed of light,” says co-author James Miller-Jones from the Curtin University node of the International Centre for Radio Astronomy Research in Perth, Australia.

“Moreover, the presence of heavy atomic nuclei in black hole jets means that mass and energy are being carried away from the black hole in much larger amounts than we previously thought, which may have an impact on the mechanism and rate by which the black hole accretes matter,” adds co-author Simone Migliari from the University of Barcelona, Spain.

Astounding new findings? Well… yeah. For a typical stellar-mass black hole, this is the first time that heavy nuclei has been detected within the jets. As of the present, there is only “one other X-ray binary that shows similar signatures from atomic nuclei in its jets – a source known as SS 433. This black hole system, however, is characterised by an unusually high accretion rate, which makes it difficult to compare its properties to those of more ordinary black holes.” Through these new observations of 4U1630–47, astronomers will be able to fill in information gaps about what causes jets to occur in black hole accretion disks and what drives them.

“While we now know a great deal about black holes and what happens around them, the formation of jets is still a big puzzle, so this observation is a major step forward in understanding this fascinating phenomenon,” says Norbert Schartel, ESA’s XMM-Newton Project Scientist.

Original Story Source: ESA Press Release.

November 13, 2013December 23, 2015 by Shannon Hall

Sgr A* Could Be a Relic of a Powerful AGN

The early universe was sizzling with active galactic nuclei (AGN) — intensely luminous cores powered by supermassive black holes — most of which could outshine their entire host galaxies and be seen across the observable universe.

While our central supermassive black hole Sgr A* lies rather dormant at the moment, new evidence suggests that it too was once a powerful AGN.

The first hint occurred two years ago when astronomers discovered Fermi bubbles — massive lobes of high-energy radiation that expand 30,000 light years north and south of the galactic center.

Of course the source of these bubbles is “a hot topic today,” Dr. Joss Hawthorn from the Sydney Institute for Astronomy and lead author on the paper, told Universe Today. “Some think the bubbles were inflated by powerful star formation in the disk, others, like me, (think) that they were inflated by a powerful jet from Sgr A*.”

It’s becoming more and more plausible that the Fermi bubbles were created by a recently powerful jet protruding from the center of our galaxy — demonstrating they are remnants of a much more violent past.

But astronomers from the Sydney Institute for Astronomy in Australia, the University of Colorado, Boulder, and the University of Cambridge have found further evidence linking Sgr A* to a recent AGN.

The Magellanic Stream — a long ribbon of gas stretching nearly half way around the Milky Way and trailing our galaxy’s two small companion galaxies, the Magellanic Clouds — is likely to be another ancient remnant of our recent activity.

The problem is that the Magellanic Stream is extremely red. It is emitting a large number of photons that clock in at a particular wavelength: 656 nanometers. This wavelength not only falls in the visible spectrum, but corresponds to a red color.

The Magellanic Stream is emitting so much red light because it contains extremely energetic hydrogen atoms. When atoms have high-energy electrons, these electrons lose energy by emitting photons.

But astronomers cannot explain why the Magellanic Stream has so many energetic hydrogen atoms, why it is such a bright red color — unless they invoke recent AGN activity from the Milky Way galaxy.

If we assume Sgr A* was once very bright, it would have lit up the Magellanic Stream, causing hydrogen atoms to absorb energy from the incoming light — an effect still visible millions of years later.

A huge outburst of energy in our recent past is likely the cause of a Seyfert flare — an eruption of light and radiation when small clouds of gas fall onto the hot disk of matter that swirls around the black hole.

“If you hurl a bucket of water into a sink, you would be shocked if it all disappeared down the plug hole. Of course, the water spins around the plughole first. (The) same thing (occurs) with gas falling onto a black hole. the spinning disk heats up and generates powerful outbursts: Seyfert flares,” Dr. Hawthorn explained.

This provides further evidence that Sgr A* was once a very powerful AGN, causing Fermi bubbles and a brighter Magellanic Stream. It’s likely it was active as recent as one to three million years ago.

The paper has been published in the Astrophysical Journal and is available for download here.

November 6, 2013December 23, 2015 by Jason Major

Early Supermassive Black Holes First Formed as Twins

Two nascent black holes formed by the collapse of an early supergiant star. From a visualization by by Christian Reisswig (Caltech).

It’s one of the puzzles of cosmology and stellar evolution: how did supermassive black holes get so… well, supermassive… in the early Universe, when seemingly not enough time had yet passed for them to accumulate their mass through steady accretion processes alone? It takes a while to eat up a billion solar masses’ worth of matter, even with a healthy appetite and lots within gravitational reach. But yet there they are: monster black holes are common within some of the most distant galaxies, flaunting their precocious growth even as the Universe was just celebrating its one billionth birthday.

Now, recent findings by researchers at Caltech suggest that these ancient SMBs were formed by the death of certain types of primordial giant stars, exotic stellar dinosaurs that grew large and died young. During their violent collapse not just one but two black holes are formed, each gathering its own mass before eventually combining together into a single supermassive monster.

Watch a simulation and find out more about how this happens below:

From a Caltech news article by Jessica Stoller-Conrad:

To investigate the origins of young supermassive black holes, Christian Reisswig, NASA Einstein Postdoctoral Fellow in Astrophysics at Caltech and Christian Ott, assistant professor of theoretical astrophysics, turned to a model involving supermassive stars. These giant, rather exotic stars are hypothesized to have existed for just a brief time in the early Universe.

Unlike ordinary stars, supermassive stars are stabilized against gravity mostly by their own photon radiation. In a very massive star, photon radiation—the outward flux of photons that is generated due to the star’s very high interior temperatures—pushes gas from the star outward in opposition to the gravitational force that pulls the gas back in.

During its life, a supermassive star slowly cools due to energy loss through the emission of photon radiation. As the star cools, it becomes more compact, and its central density slowly increases. This process lasts for a couple of million years until the star has reached sufficient compactness for gravitational instability to set in and for the star to start collapsing gravitationally.

Previous studies predicted that when supermassive stars collapse, they maintain a spherical shape that possibly becomes flattened due to rapid rotation. This shape is called an axisymmetric configuration. Incorporating the fact that very rapidly spinning stars are prone to tiny perturbations, Reisswig and his colleagues predicted that these perturbations could cause the stars to deviate into non-axisymmetric shapes during the collapse. Such initially tiny perturbations would grow rapidly, ultimately causing the gas inside the collapsing star to clump and to form high-density fragments.

“The growth of black holes to supermassive scales in the young universe seems only possible if the ‘seed’ mass of the collapsing object was already sufficiently large.”

– Christian Reisswig, NASA Einstein Postdoctoral Fellow at Caltech

Composite image from Chandra and Hubble showing supermassive black holes in the early Universe.

These fragments would orbit the center of the star and become increasingly dense as they picked up matter during the collapse; they would also increase in temperature. And then, Reisswig says, “an interesting effect kicks in.” At sufficiently high temperatures, there would be enough energy available to match up electrons and their antiparticles, or positrons, into what are known as electron-positron pairs. The creation of electron-positron pairs would cause a loss of pressure, further accelerating the collapse; as a result, the two orbiting fragments would ultimately become so dense that a black hole could form at each clump. The pair of black holes might then spiral around one another before merging to become one large black hole.

“This is a new finding,” Reisswig says. “Nobody has ever predicted that a single collapsing star could produce a pair of black holes that then merge.”

These findings were published in Physical Review Letters the week of October 11. Source: Caltech news article by Jessica Stoller-Conrad.

October 17, 2013December 23, 2015 by Tammy Plotner

ALMA Peers Into Giant Black Hole Jets

This detailed view shows the central parts of the nearby active galaxy NGC 1433. The dim blue background image, showing the central dust lanes of this galaxy, comes from the NASA/ESA Hubble Space Telescope. The coloured structures near the centre are from recent ALMA observations that have revealed a spiral shape, as well as an unexpected outflow, for the first time. Credit: ALMA (ESO/NAOJ/NRAO)/NASA/ESA/F. Combes

Did you ever wonder what it would be like to observe what happens to a galaxy near a black hole? For all of us who remember that wonderful Disney movie, it would be a remarkable – if not hypnotic – experience. Now, thanks to the powerful observational tools of the Atacama Large Millimeter/submillimeter Array (ALMA), two international astronomy teams have had the opportunity to study the jets of black holes near their galactic cores and see just how they impact their neighborhood. The researchers have captured the best view so far of a molecular gas cloud surrounding a nearby, quiescent black hole and were gifted with a surprise look at the base of a massive jet near a distant one.

These aren’t lightweights. The black holes the astronomers are studying weigh in a several billion solar masses and make their homes at the center of nearly all the galaxies in the Universe – including the Milky Way. Once upon a time, these enigmatic galactic phenomena were busy creatures. They absorbed huge amounts of matter from their surroundings, shining like bright beacons. These early black holes thrust small amounts of the matter they took in through highly powerful jets, but their current counterparts aren’t quite as active. While things may have changed a bit with time, the correlation of black hole jets and their surroundings still play a crucial role in how galaxies evolve. In the very latest of studies, both published today in the journal Astronomy & Astrophysics, astronomers employed ALMA to investigate black hole jets at very different scales: a nearby and relatively quiet black hole in the galaxy NGC 1433 and a very distant and active object called PKS 1830-211.

“ALMA has revealed a surprising spiral structure in the molecular gas close to the center of NGC 1433,” says Françoise Combes (Observatoire de Paris, France), who is the lead author of the first paper. “This explains how the material is flowing in to fuel the black hole. With the sharp new observations from ALMA, we have discovered a jet of material flowing away from the black hole, extending for only 150 light-years. This is the smallest such molecular outflow ever observed in an external galaxy.”

Need feedback? Well, that’s exactly what this process is called. “Feedback” may enlighten us to the relationship between black hole mass and the mass of the surrounding galactic bulge. The black hole consumes gas and becomes active, but then it creates jets which purge gas from its proximity. This halts star formation and controls the growth of the central bulge. In PKS 1830-211, Ivan Marti-Vidal (Chalmers University of Technology, Onsala Space Observatory, Onsala, Sweden) and his team witnessed a supermassive black hole with a jet, “but a much brighter and more active one in the early universe. It is unusual because its brilliant light passes a massive intervening galaxy on its way to Earth, and is split into two images by gravitational lensing.”

Are supermassive black holes messy eaters? You bet. There have been occasions when a supermassive black hole will unexpectedly consume a staggering amount of mass which, in turn, turbo-charges the power of the jets and lights up the radiation output to the very pinnacle of energy output. This energy is emitted as gamma rays, the shortest wavelength and highest energy form of electromagnetic radiation. And now ALMA has, by chance, caught one of these events as it happened in PKS 1830-211.

“The ALMA observation of this case of black hole indigestion has been completely serendipitous. We were observing PKS 1830-211 for another purpose, and then we spotted subtle changes of color and intensity among the images of the gravitational lens. A very careful look at this unexpected behavior led us to the conclusion that we were observing, just by a very lucky chance, right at the time when fresh new matter entered into the jet base of the black hole,” says Sebastien Muller, a co-author of the second paper.

The main image, showing the nearby active galaxy NGC 1433, comes from the NASA/ESA Hubble Space Telescope. The coloured structures near the centre shown in the insert are from recent ALMA observations that have revealed a spiral shape, as well as an unexpected outflow, for the first time. Credit: ALMA (ESO/NAOJ/NRAO)/NASA/ESA/F. Combes

As with all astronomical observations, the key to discovery is confirmation. Did the ALMA findings show up on other telescopic observations? The answer is yes. Thanks to monitoring observations with NASA’s Fermi Gamma-ray Space Telescope, there was a definite gamma ray signature exactly where it should be. Whatever was responsible for the scaling up of radiation at ALMA’s long wavelengths was also responsible for making the light of the black hole jet flare impressively.

“This is the first time that such a clear connection between gamma rays and submillimeter radio waves has been established as coming from the real base of a black hole’s jet,” adds Sebastien Muller.

It isn’t the end of the story, however. It’s just the beginning. ALMA will continue to probe into the mysterious workings of supermassive black hole jets – both near and far. Combes and her investigative team are already observing close active galaxies with ALMA, and even a unique object cataloged as PKS 1830-211. The research will continue, and with it we may one day have answers to many questions.

“There is still a lot to be learned about how black holes can create these huge energetic jets of matter and radiation,” concludes Ivan Marti-Vidal. “But the new results, obtained even before ALMA was completed, show that it is a uniquely powerful tool for probing these jets — and the discoveries are just beginning!”

Original Story Source: ESO News Release.

October 1, 2013December 23, 2015 by Jason Major

Navigating the Cosmos by Quasar

A quasar resides in the hub of the nearby galaxy NGC 4438. Credit: NASA/ESA, Jeffrey Kenney (Yale University), Elizabeth Yale (Yale University)

50 million light-years away a quasar resides in the hub of galaxy NGC 4438, an incredibly bright source of light and radiation that’s the result of a supermassive black hole actively feeding on nearby gas and dust (and pretty much anything else that ventures too closely.) Shining with the energy of 1,000 Milky Ways, this quasar — and others like it — are the brightest objects in the visible Universe… so bright, in fact, that they are used as beacons for interplanetary navigation by various exploration spacecraft.

“I must go down to the seas again, to the lonely sea and the sky,

And all I ask is a tall ship and a star to steer her by.”

– John Masefield, “Sea Fever”

Deep-space missions require precise navigation, especially when approaching bodies such as Mars, Venus, or comets. It’s often necessary to pinpoint a spacecraft traveling 100 million km from Earth to within just 1 km. To achieve this level of accuracy, experts use quasars – the most luminous objects known in the Universe – as beacons in a technique known as Delta-Differential One-Way Ranging, or delta-DOR.

Delta-DOR uses two antennas in distant locations on Earth (such as Goldstone in California and Canberra in Australia) to simultaneously track a transmitting spacecraft in order to measure the time difference (delay) between signals arriving at the two stations.

Unfortunately the delay can be affected by several sources of error, such as the radio waves traveling through the troposphere, ionosphere, and solar plasma, as well as clock instabilities at the ground stations.

Delta-DOR corrects these errors by tracking a quasar that is located near the spacecraft for calibration — usually within ten degrees. The chosen quasar’s direction is already known extremely well through astronomical measurements, typically to closer than 50 billionths of a degree (one nanoradian, or 0.208533 milliarcsecond). The delay time of the quasar is subtracted from that of the spacecraft’s, providing the delta-DOR measurement and allowing for amazingly high-precision navigation across long distances.

“Quasar locations define a reference system. They enable engineers to improve the precision of the measurements taken by ground stations and improve the accuracy of the direction to the spacecraft to an order of a millionth of a degree.”

– Frank Budnik, ESA flight dynamics expert

So even though the quasar in NGC 4438 is located 50 million light-years from Earth, it can help engineers position a spacecraft located 100 million kilometers away to an accuracy of several hundred meters. Now that’s a star to steer her by!

Read more about Delta-DOR here and here.

Source: ESA Operations

September 30, 2013April 26, 2016 by Elizabeth Howell

Are Black Holes Hairy, Or Better Described By Clean Physics?

Black holes are a spot in the universe where you won’t see the sun shine in, to paraphrase that 1960s rock-musical Hair. But speaking of “hair”, a group of scientists says these singularities may have matter (sometimes referred to as “hair”) that could affect how they appear.

This is a tangled concept to figure out (so to speak), so let’s unpack what the new study in Physical Review Letters means.

When black hole understanding was still in its infancy in the scientific literature, physicist John Wheeler wrote a phrase that is now famous among scientists in that field: “Black holes have no hair.” His phrase referred to how black holes are defined, which he believed came down to only two factors: their mass, and their angular momentum, or the rotation velocity of the hole. (Some sources also say electric charge was included as a third factor.)

Say you have a black hole that was created out of a huge star that imploded. Even though the star itself had distinctive properties, this theory says they would vanish in a black hole. So to take that to a generality, Wheeler’s phrase said all black holes are essentially the same.

Where is the Nearest Black Hole — Artist concept of matter swirling around a black hole. (NASA/Dana Berry/SkyWorks Digital)

This understanding of black holes dates back to 1963, arising back to a “clean” black hole model first published by Roy Kerr. The new study agrees that Kerr’s work from 50 years ago works with general relativity, a theory from Einstein that (in very simple terms) says the laws of nature are consistent throughout the universe. (More at this past Universe Today article.) As the theory pertains to black holes, strong sources of gravity bend space and time.

Kerr’s theory, however, does not agree with extensions of Einstein’s work, the scientists said. These extensions are known as scalar-tensor theories and there are several variations on this topic. The physics deals with the interactions between two different types of fields, scalar and tensor. Scalar fields, according to this Massachusetts Institute of Technology paper, assign values for every point of space observed. (Think a temperature map of Mars). Tensor fields measure these variables with relation to each other.

This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). New observations using the Very Large Telescope Interferometer at ESO’s Paranal Observatory in Chile have revealed not only the torus of hot dust around the black hole but also a wind of cool material in the polar regions. Credit: ESO/M. Kornmesser — This artist’s impression shows the surroundings of the supermassive black hole at the heart of the active galaxy NGC 3783 in the southern constellation of Centaurus (The Centaur). Credit: ESO/M. Kornmesser

The science team included Thomas Sotiriou, a physicist at the International School for Advanced Studies in Italy.

His team, Sotiriou said in a statement, “focused on the matter that normally surrounds realistic black holes, those observed by astrophysicists. This matter forces the pure and simple black hole hypothesized by Kerr to develop a new ‘charge’ (the hair, as we call it) which anchors it to the surrounding matter, and probably to the entire universe.

“According to our calculations,” he added, “the growth of the black hole’s hair is accompanied by the emission of distinctive gravitational waves.”

This model hasn’t been proved yet in by measurements, so this will be something for astronomical instruments to watch for in the coming decades. It also should be noted that other scientists have found different problems with the clean black-hole theory, which you can check out if you’re so inclined.

In the meantime, you can read the new study at this link. There is also a prepublished version available.

Source: Scuola Internzaionale Superiore di Studi Avanzati

September 27, 2013March 16, 2017 by Fraser Cain

How Do Black Holes Form?

Black holes are the most exotic and awe inspiring objects in the Universe.

Take the mass of an entire star. Compress it down into an object so compact that the force of gravity defies comprehension.

Nothing, not even light, can escape the pull of gravity from a black hole.

The idea was first conceived in the 18th century by the geologist John Mitchell. He realized that if you could compress the Sun down by several orders of magnitude, it would have gravity so strong that you’d need to be going faster than the speed of light to escape it.

Initially, black holes were considered nothing more than abstract mathematical concepts; even Einsten assumed they didn’t actually exist. But in 1931, the astronomer Chandrasekhar calculated that certain high mass stars might be able to collapse into black holes after all.

They turned out to be real, and over the next few decades, astronomers found many examples out in the Universe.

Stars are held in perfect balance by two opposing forces. There’s the inward pressure of gravity, attempting to collapse the star, counteracted by the outward pressure of the emitted radiation.

This artist's concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech — This artist’s concept illustrates a supermassive black hole with millions to billions times the mass of our sun. Supermassive black holes are enormously dense objects buried at the hearts of galaxies. Image credit: NASA/JPL-Caltech

At the core, millions of tonnes of hydrogen are being converted into helium every second, releasing gamma radiation. This fusion process is an exothermic reaction, meaning it releases more energy than it requires.

As the star consumes the last of its hydrogen, it switches to the stockpiles of helium that it has built up. After it runs out of helium, it switches to carbon, and then oxygen.

Since the star continues to pump out radiation, it balances out the gravitational forces trying to compress it.

Stars with the mass of our Sun pretty much stop there. Not massive enough to continue the fusion reaction, beyond oxygen, they become a white dwarf and cool down.

But for stars with about 5 times the mass of our Sun, the fusion process continues further up the periodic table to silicon, aluminum, potassium, and so on, all the way to iron.

No energy can be produced by fusing iron atoms together. It’s the stellar equivalent of ash.

And so, in a fraction of a second, the radiation from the star turns off. Without that outward pressure from the radiation, gravity wins out and the star implodes. An entire star’s mass collapses down into a smaller and smaller volume of space.

The velocity you would need to escape from the star goes up, until not even light is going fast enough to escape.

And this is how you form a black hole.

Well, that’s the main way.

You can also get black holes when dense objects, like neutron stars, collide with one another.

And then there are the supermassive black holes at the heart of every galaxy. And to be honest, astronomers still don’t know how those monsters formed.

September 25, 2013December 23, 2015 by Nancy Atkinson

Webcast: What Happens When You Fall Into a Black Hole?

An illustration of one of the zany metaphors about the black hole firewall paradox. Credit: Maki Naro via Txchnologist.

What happens if you fall into a black hole? According to Einstein’s general theory of relativity, the fall would be uneventful, until at some point the force of gravity would rip you apart. But a new theory suggests a different fate — and if correct, could challenge our understanding of gravity and how the universe works. Join the folks from the Kavli Foundation today, September 25, at 19:00 UTC (3 pm EDT, Noon PDT) as they host a live discussion and Q & A session about the latest theories about matter entering a black hole, and how these ideas are prompting researchers to reconsider our understanding of gravity.

They’ll be discussing the “blackhole firewall paradox” that you may have been hearing about lately.

You can watch live below. To submit questions ahead of time or during the webcast, send an email to [email protected] or post on Twitter with hashtag #KavliLive.

This fun graphic above refers to the recent article written by Dennis Overbye of the New York Times, “A Black Hole Mystery Wrapped in a Firewall Paradox.” The graphic was done by illustrator Maki Naro, sent to us via the Txchnologist blog’s Zany Science Metaphors.

You can see more information about the webcast at the Kavli Foundation website.

The panelists for the discussion includes Raphael Bousso (U.C. Berkeley), Juan Maldacena (Princeton University), Joseph Polchinski (Kavli Institute for Theoretical Physics at U.C. Santa Barbara), and Leonard Susskind (Stanford University).

September 18, 2013May 8, 2017 by Elizabeth Howell

Goodbye Big Bang, Hello Black Hole? A New Theory Of The Universe’s Creation

Artist's conception of the event horizon of a black hole. Credit: Victor de Schwanberg/Science Photo Library

Could the famed “Big Bang” theory need a revision? A group of theoretical physicists suppose the birth of the universe could have happened after a four-dimensional star collapsed into a black hole and ejected debris.

Before getting into their findings, let’s just preface this by saying nobody knows anything for sure. Humans obviously weren’t around at the time the universe began. The standard theory is that the universe grew from an infinitely dense point or singularity, but who knows what was there before?

“For all physicists know, dragons could have come flying out of the singularity,” stated Niayesh Afshordi, an astrophysicist with the Perimeter Institute for Theoretical Physics in Canada who co-authored the new study.

So what are the limitations of the Big Bang theory? The singularity is one of them. Also, it’s hard to predict why it would have produced a universe that has an almost uniform temperature, because the age of our universe (about 13.8 billion years) does not give enough time — as far as we can tell — to reach a temperature equilibrium.

Most cosmologists say the universe must have been expanding faster than the speed of light for this to happen, but Ashford says even that theory has problems: “The Big Bang was so chaotic, it’s not clear there would have been even a small homogenous patch for inflation to start working on.”

Representation of the timeline of the universe over 13.7 billion years, from the Big Bang, through the cosmic dark ages and formation of the first stars, to the expansion in the universe that followed. Credit: NASA/WMAP Science Team.

This is what the physicists propose:

The model they constructed has the three-dimensional universe floating as a membrane (or brane) in a “bulk universe” that has four dimensions. (Yes, this is making our heads hurt as well, so it might be easier to temporarily think of the brane as two-dimensional and the “bulk universe” as three-dimensional when trying to picture it.) You can read the more technical details in this 2000 paper on which the new theory is based.
So if this “bulk universe” has four-dimensional stars, these stars could go through the same life cycles as the three-dimensional ones we are familiar with. The most massive ones would explode as supernovae, shed their skin and have the innermost parts collapse as a black hole.
The 4-D black hole would have an “event horizon” just like the 3-D ones we are familiar with. The event horizon is the boundary between the inside and the outside of a black hole. There are a lot of theories of what goes on inside a black hole, although nothing has ever been observed.
In a 3-D universe, the event horizon appears as a two-dimensional surface. So in a 4-D universe, the event horizon would be a 3-D object called a hypersphere.
So basically, what the model says is when the 4-D star blows apart, the leftover material would create a 3-D brane surrounding a 3-D event horizon, and then expand.

The long and the short of it? To bring this back to things that we can see, it is clear from observations that the universe is expanding (and indeed is getting faster as it expands, possibly due to the mysterious dark energy). The new theory says that the expansion comes from this 3-D brane’s growth. But there is at least one limitation.

While the model does explain why the universe has nearly uniform temperature (the 4-D universe preceding it would have existed it for much longer), a European Space Agency telescope called Planck recently mapped small temperature variations in the cosmic microwave background, which is believed to be leftovers of the universe’s beginnings. (Read more about the CMB here.)

The new model differs from these CMB readings by about four percent, so the researchers are looking to refine the model. They still feel the model has worth, however. Planck shows that inflation is happening, but doesn’t show why the inflation is happening.

“The study could help to show how inflation is triggered by the motion of the universe through a higher-dimensional reality,” the researchers stated.

You can read more about their research on this prepublished Arxiv paper. The Arxiv entry does not specify if the paper has been submitted to any peer-reviewed scientific journals for publication.

Source: Nature