Star Formation Extinguished by Quasars

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According to new research, a galaxy with a quasar in the middle is not a good place to grow up. As active galactic nuclei (AGN) evolve, they pass through a “quasar phase”, where the accretion disk surrounding the central black hole blasts intense radiation into space. The quasar far outshines the entire host galaxy. After the quasar phase, when the party is over, it is as if there is no energy left and star formation stops.

AGN are the compact, active and bright central cores to active galaxies. The intense brightness from these active galactic cores is produced by the gravitationally driven accretion disk of hot matter spinning and falling into a supermassive black hole at the centre. During the lifetime of an AGN, the black hole/accretion disk combo will undergo a “quasar phase” where intense radiation is blasted from the superheated gases surrounding the black hole. Typically quasars are formed in young galaxies.
Multicolour SDSS optical images of NGC5806 and NGC5750, nearby spiral galaxies with active nuclei similar to those being studied by Westoby and his collaborators. Image credit: The Sloan Digital Sky Survey
Although the quasar phase is highly energetic and tied with young galaxy formation, according to new results from the Sloan Digital Sky Survey, it also marks the end for any further star birth in the galaxy. These findings will be presented today (Friday 4th April) at the RAS National Astronomy Meeting in Belfast, Northern Ireland, by Paul Westoby having just completed a study of 360 000 galaxies in the local Universe. He carried out this research with Carole Mundell and Ivan Baldry from the Astrophysics Research Institute of Liverpool, John Moores University, UK. This study was proposed to understand the relationship between accreting black holes, the birth of stars in galactic cores and the evolution of galaxies as a whole. The results are astonishingly detailed.

By analysing so many galaxies, quite a detailed picture emerges. The primary result to come from this shows that as a young galactic core is dominated by a highly energetic quasar, star formation stops. After this phase in a galaxy’s life, star formation is not possible; the remaining stars are left to evolve by themselves.

An artists impression of a quasar (credit: NASA)

It is believed that all AGNs go through the quasar phase in their early galactic lives. It is also thought that most massive galaxies will have a supermassive black hole hiding inside their galactic cores passively, having already gone through the quasar phase. Westoby notes that some dormant supermassive black holes can be “reignited” into a secondary quasar phase, but the mechanisms behind this are sketchy.

The starlight from the host galaxy can tell us much about how the galaxy has evolved […] Galaxies can be grouped into two simple colour families: the blue sequence, which are young, hotbeds of star-formation and the red sequence, which are massive, cool and passively evolving..” – Paul Westoby.

It is found there is a sudden cut-off point for star formation, and this occurs right after the quasar phase. After the quasar phase, the AGN relaxes into a quieter state, there is no star formation and gradual evolution of stars progresses into the “red sequence” of star evolution.

Other findings include the indication that regardless of the size of the galaxy, it is the shape of the galactic “bulge” that matters. Without a large classical bulge in the centre, supermassive black holes that drive the AGN are not possible. Therefore, only galaxies with a bulge have AGN at the core. Another factor affecting supermassive black hole formation is the density of galaxies in a volume of space. Should there be too many, supermassive black holes become a scarcity.

Source: The RAS National Astronomy Meeting 2008

A Black Hole Observed in the Heart of Mysterious Omega Centauri

Omega Centauri is a strange thing. It’s been classified as a star, then a nebula, then a globular cluster and now it’s thought to be a dwarf galaxy missing its outer stars. Why is it in such a mess? How can this oddball galaxy be explained? New research suggests it has an intermediate-black hole living in its core, giving astronomers the best idea yet as to where supermassive black holes come from. Omega Centauri might hold one of the most profound secrets as to how the largest objects in the observable universe are born…

The stars within Omega Centauri (credit: ESA/NASA)
Two thousand years ago, Omega Centauri was classified as a single star by Ptolemy. Edmond Halley studied this “star” but thought it looked a bit diffuse and re-classified it as a nebula in 1677. Then, in the 1830s, John Herschel was the first astronomer to realize this “nebula” was actually a galaxy, a globular cluster galaxy. But now, new observations by the Hubble Space Telescope (HST) reveal that this “globular cluster” isn’t what it seems… it’s actually a dwarf galaxy, stripped of its outer stars, some 17,000 light years away.

See an observation video zooming into the location of Omega Centauri in the constellation of Centaurus.

So what led to astronomers thinking there was something strange about this cosmic collection of stars? It rotates faster than other globular clusters, it is strangely flat and it contains stars of many generations (globular clusters usually contain stars of one generation). These reasons plus the fact Omega Centauri is ten times bigger than the largest globular clusters have led scientists to believe that this was no ordinary galaxy.

The constellation of Centaurus, where the globular cluster Omega Centauri is located (credit: ESA/NASA)

The main theory is that this unlucky galaxy may have crashed into the Milky Way in the distant past, shedding its outermost stars during the collision. This explains the lack of stars in its outer region. But why is it rotating so quickly, especially in the center?

These stunning images were taken by the NASA/ESA Hubble Space Telescope, which continues to do amazing science after 18 years in orbit. Combined with ground-based observations by the Gemini South telescope in Chile, astronomers have been able to deduce that a black hole may be at the root of a lot of the anomalies seen in Omega Centauri.

The research carried out at the Max-Planck Institute for Extraterrestrial Physics (in Garching, Germany), headed by Eva Noyola, shows stars near the center of Omega Centauri orbiting something very fast. In fact, this something is invisible for a reason. Calculating this invisible object’s mass, it is most likely that the group are observing an intermediate-size black hole with the mass of 40,000 solar masses. They have investigated other possibilities, perhaps the fast-orbiting stars could be accelerated by the collective mass of small, weakly radiating bodies such as white dwarves, or the orbiting stars’ have highly elliptical orbits and the point of closest approach is currently being observed, giving the impression they are going faster. However, the intermediate-size black hole theory appears to fit the situation far better.

This is a highly significant discovery, as so far there has been little linking the smaller, stellar black holes with the supermassive ones that sit in the center of large galaxies such as our own. There have been many theories put forward about how these huge black holes may have formed, but to find an intermediate-sized black hole may be the missing link and will help astrophysicists understand how supermassive black holes are “seeded” in the first place.

This result shows that there is a continuous range of masses for black holes, from supermassive, to intermediate-mass, to small stellar mass types […] We may be on the verge of uncovering one possible mechanism for the formation of supermassive black holes. Intermediate-mass black holes like this could be the seeds of full-sized supermassive black holes.” – Eva Noyola.

Source: SpaceTelescope.org

Astronomers Find the Smallest Black Hole

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Black holes seem to have no upper limit; some weigh in at hundreds of millions of times the mass of the Sun. But how small can they be? Astronomers have discovered what they think is the least massive black hole ever seen, with a mere 3.8 times the mass of the Sun, and a diameter of only 25 km (15 miles) across.

The announcement was made by Nikolai Shaposhnikov of NASA’s Goddard Space Flight Center and his colleagues at the American Astronomical Society High-Energy Astrophysics Division currently being held in Los Angeles, California.

The “tiny” black hole, known as XTE J1650-500, was discovered back in 2001 in a binary system with a normal star. Astronomers had known about the binary system for several years, but they were finally able to make accurate measurements using NASA’s Rossi X-ray Timing Explorer (RXTE) to pin down the mass.

Although black holes themselves are invisible, they’re often surrounded by a disk of hot gas and dust – material chokes up, like water going down the drain. As the hot gas builds up, it releases torrents of X-rays at regular intervals.

Astronomers have long suspected that the frequency of these X-ray blasts depend on the mass of the stars. As the mass of the black hole increases, the size of the accretion disk expands outward too; there are less frequent X-ray emissions.

By cross referencing this method with other, established techniques for weighing black holes, the team is very confident that they’ve got the trick to measuring black hole mass.

When they applied their technique to XTE J1650-500, they turned up a mass of 3.8 Suns, give or take half a solar mass. This is dramatically smaller than the previous record holder at 6.3 Suns.

What’s the smallest possible black hole? Astronomers think it’s somewhere between 1.7 and 2.7 solar masses. Smaller than that and you get a neutron star. Finding black holes that approach this lower limit will help physicists better understand how matter behaves when its crushed down in this extreme environment.

Original Source: NASA News Release

When Black Holes Explode: Measuring the Emission from the Fifth Dimension

Exploding primordial black holes could be detected (credit: Wired.com)

Primordial black holes are remnants of the Big Bang and they are predicted to be knocking around in our universe right now. If they were 1012kg or bigger at the time of creation, they have enough mass to have survived constant evaporation from Hawking radiation over the 14 billion years since the beginning of the cosmos. But what happens when the tiny black hole evaporates so small that it becomes so tightly wrapped around the structure of a fifth dimension (other than the “normal” three spatial dimensions and one time dimension)? Well, the black hole will explosively show itself, much like an elastic band snapping, emitting energy. These final moments will signify that the primordial black hole has died. What makes this exciting is that researchers believe they can detect these events as spikes of radio wave emissions and the hunt has already begun…

Publications about primordial black holes have been very popular in recent years. There is the possibility that these ancient singularities are very common in the Universe, but as they are predicted to be quite small, their effect on local space isn’t likely to be very observable (unlike younger, super-massive black holes at the centre of galaxies or the stellar black holes remaining after supernovae). However, they could be quite mischievous. Some primordial black hole antics include kicking around asteroids if they pass through the solar system, blasting through the Earth at high velocity, or even getting stuck inside a planet, slowly eating up material like a planetary parasite.

But say if these big bang relics never come near the Earth and we never see their effect on Earth (a relief, we can do without a primordial black hole playing billiards with near Earth asteroids or the threat of a mini black hole punching through the planet!)? How are we ever going to observe these theoretical singularities?

Eight-meter-wavelength Transient Array (credit: Virginia Tech)

Now, the ultimate observatory has been realized, but it measures a fairly observable cosmic emission: radio waves. The Eight-meter-wavelength Transient Array (ETA) run by Virginia Tech Departments of Electrical & Computer Engineering and Physics, and the Pisgah Astronomical Research Institute (PARI), is currently taking high cadence radio wave observations and has been doing so for the past few months. This basic-looking antenna system, in fields in Montgomery County and North Carolina, could receive emissions in the 29-47 MHz frequencies, giving researchers a unique opportunity to see primordial black holes as they die.

Interestingly, if their predictions are correct, this could provide evidence for the existence of a fifth dimension, a dimension operating at scales of billionths of a nanometer. If this exotic emission can be received, and if it is corroborated by both antennae, this could be evidence of the string theory prediction that there are more dimensions than the four we currently understand.

The idea we’re exploring is that the universe has an imperceptibly small dimension (about one billionth of a nanometer) in addition to the four that we know currently. This extra dimension would be curled up, in a state similar to that of the entire universe at the time of the Big Bang.” – Michael Kavic, project investigator.

As black holes are wrapped around this predicted fifth dimension, as they slowly evaporate and lose mass, eventually primordial black holes will be so stressed and stretched around the fifth dimension that the black hole will die, blasting out emissions in radio wave frequencies.

String theory requires extra dimensions to be a consistent theory. String theory suggests a minimum of 10 dimensions, but we’re only considering models with one extra dimension.” – Kavic

When the Large Hadron Collider goes online in May, it is hoped that the high energies generated may produce mini-black holes (amongst other cool things) where research can be done to look for the string theory extra dimensions. But the Eight-meter-wavelength Transient Array looking for the death of “naturally occurring” primordial black holes is a far less costly endeavour and may achieve the same goal.

Here’s an article on a theory that there could be 10 dimensions.

Source: Nature

Greedy Supermassive Black Holes Dislike Dark Matter

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It is widely accepted that supermassive black holes (SMBHs) sit in the centre of elliptical galaxies or bulges of spiral galaxies. They suck in as much matter as possible, generating blasts of radiation. Stars, gas and everything else nearby forms a compact “halo” and then falls to a gravitationally enforced death spiral. The greedy nature and the sheer size of these black holes have led to the idea that dark matter may supply (or may have supplied) the SMBH with some mass during its evolution. But could it be that dark matter may not be significantly involved after all? This might be one cosmic phenomenon dark matter can’t be blamed for…

Black hole accretion disks are compact halos created as dust, gas and other debris are pulled toward a black hole event horizon. Accretion disks radiate electromagnetic radiation, and the frequency of which depends on the mass of the black hole. The more massive it is, the higher the energy of radiation emitted into space. In the case of a SMBH, the huge mass causes very bright emission as the matter from the accretion disk falls into the event horizon (the point at which gravity becomes so strong that even light cannot escape). As accretion disk matter falls toward the event horizon, approximately 10% of the mass is converted into energy and ejected as X-rays. This is a far more efficient energy conversion rate than the most efficient nuclear fusion reaction (approximately 0.5%). This X-ray emission can then be observed, creating a quasar, signifying a SMBH is driving the active galaxy.
A simulation of an accretion disk (credit: Michael Owen, John Blondin, North Carolina State Univ.)
Interestingly, an SMBH is not thought to be formed from single dead massive star. They are thought to have been created from a “seed” and then grown over billions of years. The source of the mass feeding the growing SMBH comes from its accretion disk, but it is uncertain what form the matter comes in and at what rate it “feeds” the black hole. There are several possibilities as to how the largest black holes were seeded, but two are the most widely accepted:

  • Intermediate black holes (with masses of several thousand Suns) are created by vast clouds which collapse to a single point. Black holes form and accretion disks grow.
  • Massive primordial stars (the first stars, formed only 200 million years after the Big Bang) of a few hundred Sun masses may have collapsed to create smaller black holes, again forming accretion disks and growing over billions of years.

The mechanisms affecting the rate of accretion disk growth are not so clear-cut. Some theories suggest that huge quantities (most of the black hole mass) comes from dark matter. However, as dark matter is “non-baryonic” (i.e. the opposite to baryonic matter – the matter we know, love and observe in our universe) it will emit very little radiation as it falls into the black hole event horizon. If this is the case, SMBHs would grow disproportionately when compared with radiation emitted from galactic centres (only baryonic particles will emit X-rays).

New research headed by Sebastien Peirani (at the Institut d’Astrophysique de Paris, France) suggests only a very small fraction of a SMBH is composed from dark matter as it evolved. Dark matter is predicted to be collisionless and will be scattered very easily by baryonic gas clouds and stars. It seems unlikely that dark matter will be able to stay inside the black hole’s accretion disk for very long before it is repelled by all the “normal” matter being pulled toward the event horizon.

By modelling a “typical” accretion disk and comparing the results with observations of quasar luminosity, the French group found that most of the matter fuelling the SMBHs is relativistic baryonic matter. At a critical distance, outside the black hole, baryonic matter from the accretion disk is accelerated to a significant fraction of the speed of light, emitting radiation. Comparing this with simulations of a collisionless disk (i.e. the characteristics of dark matter), the baryonic model fits observations the best.

Application of our results to black hole seeds hosted by halos issued from cosmological simulations indicate that dark matter contributes to no more than [approx.] 10% of the total accreted mass, confirming that the bolometric quasar luminosity is related to the baryonic accretion history of the black hole.” – Abstract from “Dark Matter Accretion into Supermassive Black Holes

Source: arXiv

What Happens When Supermassive Black Holes Collide?

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As galaxies merge together, you might be wondering what happens with the supermassive black holes that lurk at their centres. Just imagine the forces unleashed as two black holes with hundreds of millions of times the mass of the Sun come together. The answer will surprise you. Fortunately, it’s an event that we should be able to detect from here on Earth, if we know what we’re looking for.

Most, if not all, galaxies in the Universe seem to contain supermassive blackholes. Some of the biggest can contain hundreds of millions, or even billions of times the mass of our own Sun. And the environments around them can only be called “extreme”. Researchers think that many could be spinning at the maximum rates predicted by Einstein’s theories of relativity – a significant fraction of the speed of light.

As two galaxies merge, their supermassive black holes have to eventually interact. Either through a direct collision, or by spiraling inward until they eventually merge as well.

And that’s when things get interesting.

According to simulations made by G.A. Shields from the University of Texas, Austin, and E.W. Bonning, from Yale University, the result is often a powerful recoil. Instead of coming together nicely, the forces are so extreme that one black holes is kicked away at a tremendous velocity.

The maximum kick happens with the two black holes are spinning in opposite directions, but they’re on the same orbital plane – imagine two spinning tops coming together. In a fraction of a second, one black hole is given enough of a kick to send it right out of the newly merged galaxy, never to return.

As one black hole is given a kick, the other receives a tremendous amount of energy, injected into the disk of gas and dust surrounding it. The accretion disk will blaze with a soft X-ray flare that should last thousands of years.

So even though mergers between supermassive black holes are extremely rare events, the afterglow lasts long enough that we should be able to detect a large number out there in space right now. The researchers estimate that there could be as many as 100 of these recent recoil events happening within 5 billion light-years of the Earth.

Their recently updated journal article, entitled Powerful Flares from Recoiling Black Holes in Quasars will be published in an upcoming issue of the Astrophysics Journal.

Original Source: Arxiv

Could Primordial Black Holes Deflect Asteriods on a Collision Course with Earth?

An artists impression of an asteroid belt. Credit: NASA

Primordial black holes (PBHs) are getting mischievous again. These artefacts from the Big Bang could be responsible for hiding inside planets or stars, they may even punch a neat, radioactive hole through the Earth. Now, they might start playing interplanetary billiards with asteroids in our solar system.

Knocking around lumps of rock may not sound very threatening when compared with the small black holes’ other accolades, but what if a large asteroid was knocked off course and sent in our direction? This could be one of the most catastrophic events yet to come from a PBH passing through our cosmic neighborhood…

As a race, we are constantly worried about the threat of asteroids hitting Earth. What if another large asteroid – like the one that possibly killed the dinosaurs around 65 million BC or the one that blew up over Tunguska in 1908 – were to come hurtling through space and smash into the Earth? The damage caused by such an impact could devastate whole nations, or plunge the world as we know it to the brink of extinction.

But help is at hand. From the combined efforts by groups such as NASAs Near Earth Object Program and international initiatives, governments and institutions are beginning to take this threat seriously. Tracking threatening Near Earth Asteroids is a science in itself, and for now at least, we can relax. There are no massive lumps of rock coming our way (that we know of). The last scare was a comparatively small asteroid called “2008 CT1” which came within 135,000 km of the Earth (about a third of the distance to the Moon) on February 5th, but there are no others forecast for some time.

So, we now have NEO monitoring down to a fine art – we are able to track and calculate the trajectory of observed asteroids throughout the solar system to a very high degree of accuracy. But what would happen if an asteroid should suddenly change direction? This shouldn’t happen right? Think again.

A researcher from the Astro Space Center of the P. N. Lebedev Physics Institute in Moscow has published works focusing on the possibility of asteroids veering off course. And the cause? Primordial black holes. There seems to be many publications out there at the moment musing what would happen should these black holes exist. If they do exist (and there is a high theoretical possibility that they do), there’s likely to be lots of them. So Alexander Shatskiy has gotten to the task of working out the probability of a PBH passing through the solar systems asteroid belts, possibly kicking an asteroid or two across Earths orbit.

Shatskiy finds that PBHs of certain masses are able to significantly change an asteroids orbit. There are estimates of just how big these PBHs can be, the lower limit is set by black hole radiation parameters (as theorized by Stephen Hawking), having little gravitational effect, and the upper limit is estimated to be as massive as the Earth (with an event horizon radius of an inch or so – golf ball size!). Naturally, the gravitational influence by the latter will be massive, greatly affecting any piece of rock as it passes by.
Real-time map of the distribution of thousands of known asteroids around the inner solar system. Red and yellow dots represent high risk NEOs (credit: Armagh Observatory)
Should PBHs exist, the probability of finding one passing though the solar system will actually be quite high. But what is the probability of the PBH gravitationally scattering asteroids as it passes? If one assumes a PBH with a mass corresponding to the upper mass estimate (i.e. the mass of the Earth), the effect of local space would be huge. As can be seen from an asteroid map (pictured), there is a lot of rocky debris out there! So something with the mass of the Earth barrelling through and scattering an asteroid belt could have severe consequences for planets nearby.

Although this research seems pretty far-fetched, one of the calculations estimate the average periodicity of a large gravitationally disturbed asteroids falling to Earth should occur every 190 million years. According to geological studies, this estimate is approximately the same.

Shatskiy concludes that should small black holes cause deflection of asteroid orbits, perhaps our method of tracking asteroids may be outdated:

If the hypothesis analyzed in this paper is correct, modern methods aimed at averting the asteroid danger appear to be inefficient. This is related to the fact that their main idea is revealing big meteors and asteroids with dangerous orbits and, then, monitoring these bodies. However, if the main danger consists in abrupt changes of asteroidal orbits (because of scattering on a PBH), revealing potentially dangerous bodies is hardly possible.”

Oh dear, we might be doomed after all…

Source: arXiv

What Would Happen if a Small Black Hole Hit the Earth?

We can all guess what would happen should a massive black hole drift into our solar system… there wouldn’t be much left once the intense gravitational pull consumes the planets and starts sucking away at our Sun. But what if the black hole is small, perhaps a left over remnant from the Big Bang, passing unnoticed through our neighborhood, having no observable impact on local space? What if this small singularity falls in the path of Earths orbit and hits our planet? This strange event has been pondered by theoretical physicists, understanding how a small black hole could be detected as it punches a neat hole though the Earth…

Primordial black holes (PBHs) are a predicted product of the Big Bang. Due to the massive energy generated at the beginning of our Universe, countless black holes are thought to have been created. However, small black holes are not expected to live very long. As black holes are theorized to radiate energy, they will also lose mass (according to Stephen Hawking’s theory, Hawking Radiation), small black holes will therefore fizz out of existence very rapidly. In a well known 1975 publication by Hawking, he estimates the minimum size a black hole must be to survive until present day. The PBH would have to be at least 1012kg (that’s 1,000,000,000,000 kg) in mass when it is created. 1012kg is actually quite small in cosmic standards – Earth has a mass of 6×1024kg – so we are talking about the size of a small mountain.

So, picture the scene. The Earth (any planet for that matter) is happily orbiting the Sun. A small primordial black hole just happens to be passing through our solar system, and across Earths orbit. We are all aware of how a rocky body such as a Near Earth Asteroid would affect the Earth if it hit us, but what would happen if a small Near Earth Black Hole hit us? Theoretical physicists from the Budker Institute of Nuclear Physics in Russia, and the INTEGRAL Science Data Center in Switzerland, have been pondering this same question, and in a new paper they calculate how we might observe the event should it happen (just in case we didn’t know we had hit something!).

PBHs falling into stars or planets have been thought of before. As previously reviewed in the Universe Today, some observations of the planets and stars could be attributed to small black holes getting trapped inside the gravitational well of the body. This might explain the unusual temperatures observed in Saturn and Jupiter, they are hotter than they should be, the extra heat might be produced by interactions with a PBH hiding inside. If trapped within a star, a PBH might take energy from the nuclear reactions in the core, perhaps bringing on a premature supernova. But what if the PBH is travelling very fast and hits the Earth? This is what this research focuses on.

I’d expect some catastrophic, energetic event as a primordial black hole hits the Earth. After all, it’s a black hole! But the results from this paper are a bit of an anti-climax, but cool all the same.

By calculating where the energy from the collision may come from, the researchers can estimate what effect the collision may have. The two main sources of energy will be from the PBH actually hitting Earth material (kinetic) and from black hole radiation. Assuming we have more likelihood of hitting a micro-black hole (i.e. much, much smaller than a black hole from a collapsed star) originating from the beginning of the Universe, it is going to be tiny. Using Hawking’s 1012kg black hole as an example, a black hole of this size will have a radius of 1.5×10-15 meters… that’s approximately the size of a proton!

This may be one tiny black hole, but it packs quite a punch. But is it measurable? PBHs are theorized to zip straight through matter as if it wasn’t there, but it will leave a mark. As the tiny entity flies through the Earth at a supersonic velocity, it will pump out radiation in the form of electrons and positrons. The total energy created by a PBH roughly equals the energy produced by the detonation of one tonne of TNT, but this energy is the total energy it deposits along its path through the Earths diameter, not the energy it produces on impact. So don’t expect a magnificent explosion, we’d be lucky to see a spark as it hits the ground.

Any hopes of detecting such a small black hole impact are slim, as the seismic waves generated would be negligible. In fact, the only evidence of a black hole of this size passing through the planet will be the radiation damage along the microscopic tunnel passing from one side of the Earth to the other. As boldly stated by the Russian/Swiss team:

It creates a long tube of heavily radiative damaged material, which should stay recognizable for geological time.” – Khriplovich, Pomeransky, Produit and Ruban, from the paper: “Can one detect passage of small black hole through the Earth?

As this research focuses on a tiny, primordial black hole, it would be interesting to investigate the effects of a larger black hole would have on impact – perhaps one with the mass of the Earth and the radius of a golf ball…?

Source paper: arXiv

Synthetic Black Hole Event Horizon Created in UK Laboratory

Researchers at St. Andrews University, Scotland, claim to have found a way to simulate an event horizon of a black hole – not through a new cosmic observation technique, and not by a high powered supercomputer… but in the laboratory. Using lasers, a length of optical fiber and depending on some bizarre quantum mechanics, a “singularity” may be created to alter a laser’s wavelength, synthesizing the effects of an event horizon. If this experiment can produce an event horizon, the theoretical phenomenon of Hawking Radiation may be tested, perhaps giving Stephen Hawking the best chance yet of winning the Nobel Prize.

So how do you create a black hole? In the cosmos, black holes are created by the collapse of massive stars. The mass of the star collapses down to a single point (after running out of fuel and undergoing a supernova) due to the massive gravitational forces acting on the body. Should the star exceed a certain mass “limit” (i.e. the Chandrasekhar limit – a maximum at which the mass of a star cannot support its structure against gravity), it will collapse into a discrete point (a singularity). Space-time will be so warped that all local energy (matter and radiation) will fall into the singularity. The distance from the singularity at which even light cannot escape the gravitational pull is known as the event horizon. High energy particle collisions by cosmic rays impacting the upper atmosphere might produce micro-black holes (MBHs). The Large Hadron Collider (at CERN, near Geneva, Switzerland) may also be capable of producing collisions energetic enough to create MBHs. Interestingly, if the LHC can produce MBHs, Stephen Hawking’s theory of “Hawking Radiation” may be proven should the MBHs created evaporate almost instantly.

Hawking predicts that black holes emit radiation. This theory is paradoxical, as no radiation can escape the event horizon of a black hole. However, Hawking theorizes that due to a quirk in quantum dynamics, black holes can produce radiation.
The principal of Hawking Radiation (source: http://library.thinkquest.org)
Put very simply, the Universe allows particles to be created within a vacuum, “borrowing” energy from their surroundings. To conserve the energy balance, the particle and its anti-particle can only live for a short time, returning the borrowed energy very quickly by annihilating with each other. So long as they pop in and out of existence within a quantum time limit, they are considered to be “virtual particles”. Creation to annihilation has net zero energy.

However, the situation changes if this particle pair is generated at or near an event horizon of a black hole. If one of the virtual pair falls into the black hole, and its partner is ejected away from the event horizon, they cannot annihilate. Both virtual particles will become “real”, allowing the escaping particle to carry energy and mass away from the black hole (the trapped particle can be considered to have negative mass, thus reducing the mass of the black hole). This is how Hawking radiation predicts “evaporating” black holes, as mass is lost to this quantum quirk at the event horizon. Hawking predicts that black holes will gradually evaporate and disappear, plus this effect will be most prominent for small black holes and MBHs.

So… back to our St. Andrews laboratory…

Prof Ulf Leonhardt is hoping to create the conditions of a black hole event horizon by using laser pulses, possibly creating the first direct experiment to test Hawking radiation. Leonhardt is an expert in “quantum catastrophes”, the point at which wave physics breaks down, creating a singularity. In the recent “Cosmology Meets Condensed Matter” meeting in London, Leonhardt’s team announced their method to simulate one of the key components of the event horizon environment.

Light travels through materials at different velocities, depending on their wave properties. The St. Andrews group use two laser beams, one slow, one fast. First, a slow propagating pulse is fired down the optical fiber, followed by a faster pulse. The faster pulse should “catch up” with the slower pulse. However, as the slow pulse passes through the medium, it alters the optical properties of the fiber, causing the fast pulse to slow in its wake. This is what happens to light as it tries to escape from the event horizon – it is slowed down so much that it becomes “trapped”.

We show by theoretical calculations that such a system is capable of probing the quantum effects of horizons, in particular Hawking radiation.” – From a forthcoming paper by the St. Andrews group.

The effects that two laser pulses have on eachother to mimic the physics within an event horizon sounds strange, but this new study may help us understand if MBHs are being generated in the LHCs and may push Stephen Hawking a little closer toward a deserved Nobel Prize.
Source: Telegraph.co.uk

“Listening” for Gravitational Waves to Track Down Black Holes

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Gravitational waves are predicted by Einstein’s 1916 general theory of relativity, but they are notoriously hard to detect and it’s taken many decades to come close to observing them. Now, with the help of a supercomputer named SUGAR (Syracuse University Gravitational and Relativity Cluster), two years of data collected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) will be analyzed to find gravitational waves. Once detected, it is hoped that the location of some of the Universes most powerful collisions and explosions will be found, perhaps even hearing the distant ringing of celestial black holes…

Gravitational waves travel at the speed of light and propagate throughout the cosmos. Like ripples on the surface of a universe-sized pond, they travel away from their point of origin and should be detected as they traverse through the fabric of space-time, passing though our cosmic neighborhood. Gravitational waves are generated by massive stellar events such as supernovae (when giant stars run out of fuel and explode) or collisions between Massive Astrophysical Compact Halo Objects (MACHOs) like black holes or neutron stars. Theoretically they should be generated by any sufficiently massive body in the Universe oscillating, propagating or colliding.

The Northern leg of the LIGO Interferometer near Richland, Washington (Credit: LIGO)
LIGO, a very ambitious $365 million (National Science Foundation funded) joint project between MIT and Caltech founded by Kip Thorne, Ronald Drever and Rainer Weiss, began taking data in 2005. LIGO uses a laser interferometer to detect the passage of gravitational waves. As a wave passes through local space-time, the laser should be slightly distorted, allowing the interferometer to detect a space-time fluctuation. After two years of taking data from LIGO, the search for the gravitational wave signatures can begin. But how can LIGO detect waves being generated by black holes? This is where SUGAR comes in.

Syracuse University assistant professor Duncan Brown, with colleagues in the Simulating eXtreme Spacetimes (SXS) project (a collaboration with Caltech and Cornell University), is assembling SUGAR in the aim to simulate two black holes colliding. This is such a complex situation that a network of 80 computers, containing 320 CPUs with 640 Gigabytes of RAM is required to compute the collision and the creation of gravitational waves (as a comparison, the laptop I’m typing on has one CPU with two Gigabytes of RAM…). Brown also has 96 Terabytes of hard disk space on which to store the LIGO data SUGAR will be analyzing. This will be a massive resource for the SXS team, but it will be needed to calculate Einstein’s relativity equations.

Looking for gravitational waves is like listening to the universe. Different kinds of events produce different wave patterns. We want to try to extract a wave pattern — a special sound — that matches our model from all of the noise in the LIGO data.” – Duncan Brown

By combining the observational capabilities of LIGO and the computing power of SUGAR (characterizing the signature of black hole gravitational waves), perhaps direct evidence of gravitational waves may be found; making the first direct observations of black holes possible by “listening” to the gravitational waves they produce.

Source: Science Daily