10 Amazing Facts About Black Holes

An artists illustration of the central engine of a Quasar. These "Quasi-stellar Objects" QSOs are now recognized as the super massive black holes at the center of emerging galaxies in the early Universe. (Photo Credit: NASA)

Imagine matter packed so densely that nothing can escape. Not a moon, not a planet and not even light. That’s what black holes are — a spot where gravity’s pull is huge, ending up being dangerous for anything that accidentally strays by. But how did black holes come to be, and why are they important? Below we have 10 facts about black holes — just a few tidbits about these fascinating objects.

Fact 1: You can’t directly see a black hole.

Because a black hole is indeed “black” — no light can escape from it — it’s impossible for us to sense the hole directly through our instruments, no matter what kind of electromagnetic radiation you use (light, X-rays, whatever.) The key is to look at the hole’s effects on the nearby environment, points out NASA. Say a star happens to get too close to the black hole, for example. The black hole naturally pulls on the star and rips it to shreds. When the matter from the star begins to bleed toward the black hole, it gets faster, gets hotter and glows brightly in X-rays.

Fact 2: Look out! Our Milky Way likely has a black hole.

A natural next question is given how dangerous a black hole is, is Earth in any imminent danger of getting swallowed? The answer is no, astronomers say, although there is probably a huge supermassive black hole lurking in the middle of our galaxy. Luckily, we’re nowhere near this monster — we are about two-thirds of the way out from the center, relative to the rest of our galaxy — but we can certainly observe its effects from afar. For example: the European Space Agency says it’s four million times more massive than our Sun, and that it’s surrounded by surprisingly hot gas.

Sagittarius A in infrared (red and yellow, from the Hubble Space Telescope) and X-ray (blue, from the Chandra space telescope). Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI
Sagittarius A in infrared (red and yellow, from the Hubble Space Telescope) and X-ray (blue, from the Chandra space telescope). Credit: X-ray: NASA/UMass/D.Wang et al., IR: NASA/STScI

Fact 3: Dying stars create stellar black holes.

Say you have a star that’s about 20 times more massive than the Sun. Our Sun is going to end its life quietly; when its nuclear fuel burns out, it’ll slowly fade into a white dwarf. That’s not the case for far more massive stars. When those monsters run out of fuel, gravity will overwhelm the natural pressure the star maintains to keep its shape stable. When the pressure from nuclear reactions collapses, according to the Space Telescope Science Institute, gravity violently overwhelms and collapses the core and other layers are flung into space. This is called a supernova. The remaining core collapses into a singularity — a spot of infinite density and almost no volume. That’s another name for a black hole.

Fact 4: Black holes come in a range of sizes.

There are at least three types of black holes, NASA says, ranging from relative squeakers to those that dominate a galaxy’s center. Primordial black holes are the smallest kinds, and range in size from one atom’s size to a mountain’s mass. Stellar black holes, the most common type, are up to 20 times more massive than our own Sun and are likely sprinkled in the dozens within the Milky Way. And then there are the gargantuan ones in the centers of galaxies, called “supermassive black holes.” They’re each more than one million times more massive than the Sun. How these beasts formed is still being examined.

A binary black hole system, viewed from above. Image Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775)
A binary black hole system, viewed from above. Credit: Bohn et al. (see http://arxiv.org/abs/1410.7775)

Fact 5: Weird time stuff happens around black holes.

This is best illustrated by one person (call them Unlucky) falling into a black hole while another person (call them Lucky) watches. From Lucky’s perspective, Unlucky’s time clock appears to be ticking slower and slower. This is in accordance with Einstein’s theory of general relativity, which (simply put) says that time is affected by how fast you go, when you’re at extreme speeds close to light. The black hole warps time and space so much that Unlucky’s time appears to be running slower. From Unlucky’s perspective, however, their clock is running normally and Lucky’s is running fast.

Fact 6: The first black hole wasn’t discovered until X-ray astronomy was used.

Cygnus X-1 was first found during balloon flights in the 1960s, but wasn’t identified as a black hole for about another decade. According to NASA, the black hole is 10 times more massive to the Sun. Nearby is a blue supergiant star that is about 20 times more massive than the Sun, which is bleeding due to the black hole and creating X-ray emissions.

Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. (NASA/CXC/M.Weiss)
Illustration of Cygnus X-1, another stellar-mass black hole located 6070 ly away. Credit: NASA/CXC/M.Weiss

Fact 7: The nearest black hole is likely not 1,600 light-years away.

An erroneous measurement of V4641 Sagitarii led to a slew of news reports a few years back saying that the nearest black hole to Earth is astoundingly close, just 1,600 light-years away. Not close enough to be considered dangerous, but way closer than thought. Further research, however, shows that the black hole is likely further away than that. Looking at the rotation of its companion star, among other factors, yielded a 2014 result of more than 20,000 light years.

Fact 8: We aren’t sure if wormholes exist.

A popular science-fiction topic concerns what happens if somebody falls into a black hole. Some people believe these objects are a sort of wormhole to other parts of the Universe, making faster-than-light travel possible. But as this Smithsonian Magazine article points out, anything is possible since we still have a lot to figure out about physics. “Since we do not yet have a theory that reliably unifies general relativity with quantum mechanics, we do not know of the entire zoo of possible spacetime structures that could accommodate wormholes,” said Abi Loeb, who is with the Harvard-Smithsonian Center for Astrophysics.

Diagram of a wormhole, or theoretical shortcut path between two locations in the universe. Credit: Wikipedia
Diagram of a wormhole, or theoretical shortcut path between two locations in the universe. Credit: Wikipedia

Fact 9: Black holes are only dangerous if you get too close.

Like creatures behind a cage, it’s okay to observe a black hole if you stay away from its event horizon — think of it like the gravitational field of a planet. This zone is the point of no return, when you’re too close for any hope of rescue. But you can safely observe the black hole from outside of this arena. By extension, this means it’s likely impossible for a black hole to swallow up everything in the Universe (barring some sort of major revision to physics or understanding of our Cosmos, of course.)

Fact 10: Black holes are used all the time in science fiction.

There are so many films and movies using black holes, for example, that it’s impossible to list them all. Interstellar‘s journeys through the universe includes a close-up look at a black hole. Event Horizon explores the phenomenon of artificial black holes — something that is also discussed in the Star Trek universe. Black holes are also talked about in Battlestar: Galactica, Stargate: SG1 and many, many other space shows.

Here on Universe Today we have a great article about a practical use for black holes: as spacecraft engines. No one can get to a black hole without space travel. Astronomy Cast offers a good episode about interstellar travel.

When Two Supermassive Black Holes Merge, It’s a Galactic Train Wreck

An artist's conception of a black hole binary in a heart of a quasar, with the data showing the periodic variability superposed. Credit: Santiago Lombeyda/Caltech Center for Data-Driven Discovery

Most large galaxies harbor central supermassive black holes with masses equivalent to millions, or even billions, of Suns. Some, like the one in the center of the Milky Way Galaxy, lie quiet. Others, known as quasars, chow down on so much gas they outshine their host galaxies and are even visible across the Universe.

Although their brilliant light varies across all wavelengths, it does so randomly — there’s no regularity in the peaks and dips of brightness. Now Matthew Graham from Caltech and his colleagues have found an exception to the rule.

Quasar PG 1302-102 shows an unusual repeating light signature that looks like a sinusoidal curve. Astronomers think hidden behind the light are two supermassive black holes in the final phases of a merger — something theoretically predicted but never before seen. If the theory holds, astronomers might be able to witness two black holes en route to a collision of incredible scale.

The light curve combines data from two CRTS telescopes (CSS and MLS) with historical data from the LINEAR and ASAS surveys, and the literature15, 16 (see Methods for details). The error bars represent one standard deviation errors on the photometry values. The red dashed line indicates a sinusoid with period 1,884 days and amplitude 0.14 mag. The uncertainty in the measured period is 88 days. Note that this does not reflect the expected shape of the periodic waveform, which will depend on the physical properties of the system. MJD, modified Julian day. Image Credit: Graham et al.
The light curve combines data from two CRTS telescopes (CSS and MLS) with historical data from the LINEAR and ASAS surveys. Image Credit: Graham et al.

Graham and his colleagues discovered the unusual quasar on a whim. They were aiming to study quasar variability using the Catalina Real-Time Transient Survey (CRTS), which uses three ground-based telescopes to monitor some 500 million objects strewn across 80 percent of the sky, when 20 or so periodic sources popped up.

Of those 20 periodic quasars, PG 1302-102 was the most promising. It had a strong signal that appeared to repeat every five years or so. But what causes the repeating signal?

The black holes that power quasars do not emit light. Instead the light originates from the hot accretion disk that feeds the black hole. Orbiting clouds of gas, which are heated and ionized by the disk, also contribute in the form of visible emission lines.

“When you look at the emission lines in a spectrum from an object, what you’re really seeing is information about speed — whether something is moving toward you or away from you and how fast. It’s the Doppler effect,” said study coauthor Eilat Glikman from Middlebury College in Vermont, in a news release. “With quasars, you typically have one emission line, and that line is a symmetric curve. But with this quasar, it was necessary to add a second emission line with a slightly different speed than the first one in order to fit the data. That suggests something else, such as a second black hole, is perturbing this system.”

So a tight supermassive black hole binary is the most likely explanation for this oddly periodic quasar.

“Until now, the only known examples of supermassive black holes on their way to a merger have been separated by tens or hundreds of thousands of light years,” said study coauthor Daniel Stern from NASA’s Jet Propulsion Laboratory. “At such vast distances, it would take many millions, or even billions, of years for a collision and merger to occur. In contrast, the black holes in PG 1302-102 are, at most, a few hundredths of a light year apart and could merge in about a million years or less.”

But astronomers remain unsure about what physical mechanism is responsible for the quasar’s repeating light signal. It’s possible that one quasar is funneling material from its accretion disk into jets, which are rotating like beams from a lighthouse. Or perhaps a portion of the accretion disk itself is thicker than the rest, causing light to be blocked at certain spots in its orbit. Or maybe the accretion disk is dumping material onto the black hole in a regular fashion, causing periodic bursts of energy.

“Even though there are a number of viable physical mechanisms behind the periodicity we’re seeing — either the precessing jet, warped accretion disk or periodic dumping — these are all still fundamentally caused by a close binary system,” said Graham.

Astronomers still don’t have a good handle on what happens in the final few light-years of a black hole merger. And of course these two black holes still won’t collide for thousands to millions of years. Even watching for the period to shorten as they spiral inward would dwarf human timescales. But the discovery of a system so late in the game proves promising for future work.

The results have been published in Nature.

What Will We Never See?

What Will We Never See?

Thanks to our powerful telescopes, there are so many places in the Universe we can see. But there are places hidden from us, and places that we’ll never be able to see.

We’re really lucky to live in our Universe with our particular laws of physics. At least, that’s what we keep telling ourselves. The laws of physics can be cruel and unforgiving, and should you try and cross them, they will crush you like a bug.

Here at Universe Today, we embrace our Physics overlords and prefer to focus on the positive, the fact that light travels at the speed of light is really helpful. This allows us to look backwards in time as we look further out. Billions of light-years away, we can see what the Universe looked like billions of years ago. Physics is good. Physics knows what’s best. Thanks physics. And where the hand of physics gives, it can also take away.

There are some parts of the Universe that we’ll never, ever be able to see. No matter what we do. They’ll always remain just out of reach. No matter how much we plead, in some sort of Kafka-esque nightmare, these rules do not appear to have conscience or room for appeal.

As we look outward in the cosmos, we look backwards in time and at the very edge of our vision is the Cosmic Microwave Background Radiation. The point after the Big Bang where everything had cooled down enough so it was no longer opaque. Light could finally escape and travel through a transparent Universe. This happened about 300,000 years after the Big Bang. What happened before that is a mystery. We can calculate what the Universe was like, but we can’t actually look at it. Possibly, we just don’t have the right clearance levels.

On the other end of the timeline, in the distant distant future. Assuming humans, or our Terry Gilliam inspired robot bodies are still around to observe the Universe, there will be a lot less to see. Distance is also out to rain on our sightseeing safari. The expansion of the Universe is accelerating, and galaxies are speeding away from each other faster and faster. Eventually, they’ll be moving away from us faster than the speed of light.

What would you see at the speed of light/
What would you see at the speed of light/

When that happens, we’ll see the last few photons from those distant galaxies, redshifted into oblivion. And then, we won’t see any galaxies at all. Their light will never reach us and our skies will be eerily empty. Just don’t let physics hear a sad tone in your voice, we don’t want to spend another night in the “joy re-education camps”

Currently, we can see a sphere of the Universe that measures 92 billion light-years across. Outside that sphere is more Universe, a hidden, censored Universe. Universe that we can’t see because the light hasn’t reached us yet. Fortunately, every year that goes by, a little less Universe is redacted from the record, and the sphere we can observe gets bigger by one light-year. We can see a little more in all directions.

Finally, let’s consider what’s inside the event horizon of a black hole. A place that you can’t look at, because the gravity is so strong that light itself can never escape it. So by definition, you can’t see what absorbs all its own light. Astronomers don’t know if black holes crunch down to a physical sphere and stop shrinking, or continue shrinking forever, getting smaller and smaller into infinity. Clearly, we can’t look there because we shouldn’t be looking there. They’re terrible places. The possibility of shrinking forever gives me the heebies.

Artistic view of a radiating black hole.  Credit: NASA
Artistic view of a radiating black hole. Credit: NASA

And so, good news! The chocolate ration has been increased from 40 grams to 25 grams, and our physics overlords are good, can only do good, and always know what’s best for us. In fact, so good that gravity might actually provide us with a tool to “see” these hidden places, but only because “they” want us to.

When black holes form, or massive objects smash into each other, or there are “Big Bangs”, these generate distortions in spacetime called gravitational waves. Like gravity itself, these propagate across the Universe and could be detected.It’s possible we could use gravitational waves to “see” beyond the event horizon of a black hole, or past the Cosmic Microwave Background Radiation.

The problem is that gravitational waves are so faint, we haven’t even detected a single one yet. But that’s probably just a technology problem. In the end, we need a more sensitive observatory. We’ll get there. Alternately we could apply to the laws of physics board of appeals and fill in one of their 2500 page application forms in triplicate and see if we can be granted a rules exception, and maybe just get a tiny little peek behind that veil.

We live an amazing Universe, most of which we’ll never be able to see. But that’s okay, there’s enough we can see to keep us busy until infinity. What law of physics would you like to be granted a special exception to ignore. Tell us in the comments below.

Gamma Ray Bursts Limit The Habitability of Certain Galaxies, Says Study

An artistic image of the explosion of a star leading to a gamma-ray burst. (Source: FUW/Tentaris/Maciej Fro?ow)

Gamma ray bursts (GRBs) are some of the brightest, most dramatic events in the Universe. These cosmic tempests are characterized by a spectacular explosion of photons with energies 1,000,000 times greater than the most energetic light our eyes can detect. Due to their explosive power, long-lasting GRBs are predicted to have catastrophic consequences for life on any nearby planet. But could this type of event occur in our own stellar neighborhood? In a new paper published in Physical Review Letters, two astrophysicists examine the probability of a deadly GRB occurring in galaxies like the Milky Way, potentially shedding light on the risk for organisms on Earth, both now and in our distant past and future.

There are two main kinds of GRBs: short, and long. Short GRBs last less than two seconds and are thought to result from the merger of two compact stars, such as neutron stars or black holes. Conversely, long GRBs last more than two seconds and seem to occur in conjunction with certain kinds of Type I supernovae, specifically those that result when a massive star throws off all of its hydrogen and helium during collapse.

Perhaps unsurprisingly, long GRBs are much more threatening to planetary systems than short GRBs. Since dangerous long GRBs appear to be relatively rare in large, metal-rich galaxies like our own, it has long been thought that planets in the Milky Way would be immune to their fallout. But take into account the inconceivably old age of the Universe, and “relatively rare” no longer seems to cut it.

In fact, according to the authors of the new paper, there is a 90% chance that a GRB powerful enough to destroy Earth’s ozone layer occurred in our stellar neighborhood some time in the last 5 billion years, and a 50% chance that such an event occurred within the last half billion years. These odds indicate a possible trigger for the second worst mass extinction in Earth’s history: the Ordovician Extinction. This great decimation occurred 440-450 million years ago and led to the death of more than 80% of all species.

Today, however, Earth appears to be relatively safe. Galaxies that produce GRBs at a far higher rate than our own, such as the Large Magellanic Cloud, are currently too far from Earth to be any cause for alarm. Additionally, our Solar System’s home address in the sleepy outskirts of the Milky Way places us far away from our own galaxy’s more active, star-forming regions, areas that would be more likely to produce GRBs. Interestingly, the fact that such quiet outer regions exist within spiral galaxies like our own is entirely due to the precise value of the cosmological constant – the factor that describes our Universe’s expansion rate – that we observe. If the Universe had expanded any faster, such galaxies would not exist; any slower, and spirals would be far more compact and thus, far more energetically active.

In a future paper, the authors promise to look into the role long GRBs may play in Fermi’s paradox, the open question of why advanced lifeforms appear to be so rare in our Universe. A preprint of their current work can be accessed on the ArXiv.

“Spotters Guide” for Detecting Black Hole Collisions

A supermassive black hole has been found in an unusual spot: an isolated region of space where only small, dim galaxies reside. Image credit: NASA/JPL-Caltech
A team of astronomers from South Africa have noticed a series of supermassive black holes in distant galaxies that are all spinning in the same direction. Credit: NASA/JPL-Caltech

When it comes to the many mysteries of the Universe, a special category is reserved for black holes. Since they are invisible to the naked eye, they remain visibly undetected, and scientists are forced to rely on “seeing” the effects their intense gravity has on nearby stars and gas clouds in order to study them.

That may be about to change, thanks to a team from Cardiff University. Here, researchers have achieved a breakthrough that could help scientists discover hundreds of black holes throughout the Universe.

Led by Dr. Mark Hannam from the School of Physics and Astronomy, the researchers have built a theoretical model which aims to predict all potential gravitational-wave signals that might be found by scientists working with the Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors.

These detectors, which act like microphones, are designed to search out remnants of black hole collisions. When they are switched on, the Cardiff team hope their research will act as a sort of “spotters guide” and help scientists pick up the faint ripples of collisions – known as gravitational waves – that took place millions of years ago.

X-ray/radio composite image of two supermassive black holes spiral towards each other near the center of a galaxy cluster named Abell 400. Credit: X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et al.; Radio: NRAO/VLA/NRL
X-ray/radio composite image of two supermassive black holes spiraling towards each other near the center of Abell 400 galaxy cluster. Credit: X-ray: NASA/CXC/AIfA/D.Hudson & T.Reiprich et al.; Radio: NRAO/VLA/NRL

Made up of postdoctoral researchers, PhD students, and collaborators from universities in Europe and the United States, the Cardiff team will work with scientists across the world as they attempt to unravel the origins of the Universe.

“The rapid spinning of black holes will cause the orbits to wobble, just like the last wobbles of a spinning top before it falls over,” Hannam said. “These wobbles can make the black holes trace out wild paths around each other, leading to extremely complicated gravitational-wave signals. Our model aims to predict this behavior and help scientists find the signals in the detector data.”

Already, the new model has been programmed into the computer codes that LIGO scientists all over the world are preparing to use to search for black-hole mergers when the detectors switch on.

Dr Hannam added: “Sometimes the orbits of these spinning black holes look completely tangled up, like a ball of string. But if you imagine whirling around with the black holes, then it all looks much clearer, and we can write down equations to describe what is happening. It’s like watching a kid on a high-speed spinning amusement park ride, apparently waving their hands around. From the side lines, it’s impossible to tell what they’re doing. But if you sit next to them, they might be sitting perfectly still, just giving you the thumbs up.”

Researchers crunched Einstein's theory of general relativity on the Columbia supercomputer at the NASA Ames Research Center to create a three-dimensional simulation of merging black holes. Image Credit: Henze, NASA
Researchers crunched Einstein’s theory of general relativity on the Columbia supercomputer at the NASA Ames Research Center to create a three-dimensional simulation of merging black holes. Credit: Henze, NASA

But of course, there’s still work to do: “So far we’ve only included these precession effects while the black holes spiral towards each other,” said Dr. Hannam. “We still need to work our exactly what the spins do when the black holes collide.”

For that they need to perform large computer simulations to solve Einstein’s equations for the moments before and after the collision. They’ll also need to produce many simulations to capture enough combinations of black-hole masses and spin directions to understand the overall behavior of these complicated systems.

In addition, time is somewhat limited for the Cardiff team. Once the detectors are switched on, it will only be a matter of time before the first gravitational wave-detections are made. The calculations that Dr. Hannam and his colleagues are producing will have to ready in time if they hope to make the most of them.

But Dr. Hannam is optimistic. “For years we were stumped on how to untangle the black-hole motion,” he said. “Now that we’ve solved that, we know what to do next.”

Further Reading: News Center – Cardiff U

Review: In “Interstellar,” Christopher Nolan Shows He Has The Right Stuff

Mathew McConnaughey wades through an ocean on another planet. This is not a fishing expedition. He is out to save his children and all humanity. Image courtesy Paramount.

Science fiction aficionados, take heed. The highly-anticipated movie Interstellar is sharp and gripping. Nolan and cast show in the end that they have the right stuff. Nearly a three hour saga, it holds your attention and keeps you guessing. Only a couple of scenes seemed to drift and lose focus. Interstellar borrows style and substance from some of the finest in the genre and also adds new twists while paying attention to real science. If a science-fiction movie shies away from imagining the unknown, taking its best shot of what we do not know, then it fails a key aspect of making sci-fi. Interstellar delivers in this respect very well.

Jessica Chastain, the grown daughter of astronaut McConnaughey starts to torch the cornfields. Interstellar viewers are likely to show no sympathy to the ever present corn fields.
Jessica Chastain, the grown daughter of astronaut McConnaughey takes a torch to the cornfields. Interstellar viewers are likely to show no sympathy to the ever present corn fields. Image courtesy Paramount.

The movie begins quite unassuming in an oddly green but dusty farmland. It does not rely on showing off futuristic views of Earth and humanity to dazzle us. However, when you see a farming family with a dinner table full of nothing but variations of their cash crop which is known mostly as feedstock for swine and cattle, you know humanity is in some hard times. McConaughey! Save us now! I do not want to live in such a future!

One is left wondering about what got us to the conditions facing humanity from the onset of the movie. One can easily imagine a couple of hot topic issues that splits the American public in two. But Nolan doesn’t try to add a political or religious bent to Interstellar. NASA is in the movie but apparently after decades of further neglect, it is literally a shadow of even its present self.

Somehow, recent science fiction movies — Gravity being one exception — would make us believe that the majority of American astronauts are from the Midwest. Driving a John Deere when you are 12, being raised under big sky or in proximity to the home of the Wright Brothers would make you hell-bent to get out of Dodge and not just see the world but leave the planet. Matthew McConaughey adds to that persona.

Dr. Kip Thorne made it clear that black is not the primary hue of Black Holes. His guidance offered to Nolan raised science fiction to a new level.
Dr. Kip Thorne made it clear that black is not the primary hue of Black Holes. His guidance offered to Nolan raised science fiction to a new level. Image courtesy Paramount.

We are seemingly in the golden age of astronomy. At present, a science fiction movie with special effects can hardly match the imagery that European and American astronomy is delivering day after day. There is one of our planets that gets a very modest delivery in Interstellar. An undergraduate graphic artist could take hold of NASA imagery and outshine those scenes quite easily. However, it appears that Nolan did not see it necessary to out-do every scene of past sci-fi or every astronomy picture of the day (APOD) to make a great movie.

Nolan drew upon American astro-physicist Dr. Kip Thorne, an expert on Einstein’s General Relativity, to deliver a world-class presentation of possibly the most extraordinary objects in our Universe – black holes. It is fair to place Thorne alongside the likes of Sagan, Feynman, Clarke and Bradbury to advise and deliver wonders of the cosmos in compelling cinematic form. In Instellar, using a black hole in place of a star to hold a planetary system is fascinating and also a bit unbelievable. Whether life could persist in such a system is a open question. There is one scene that will distress most everyone in and around NASA that involves the Apollo Moon landings and one has to wonder if Thorne was pulling a good one on old NASA friends.

Great science fiction combines a vision of the future with a human story. McConaughey and family are pretty unassuming. John Lithgow, who plays grandpa, the retired farmer, doesn’t add much and some craggy old character actor would have been just fine. Michael Cane as the lead professor works well and Cane’s mastery is used to thicken and twist the plot. His role is not unlike the one in Children of Men. He creates bends in the plot that the rest of the cast must conform to.

There was one piece of advice I read in previews of Interstellar. See it in Imax format. So I ventured over to the Imax screening at the Technology Museum in Silicon Valley. I think this advice was half correct. The Earthly scenes gained little or nothing from Imax but once they were in outer space, Imax was the right stuff. Portraying a black hole and other celestial wonders is not easy for anyone including the greatest physicists of our era and Thorne and Nolan were right to use Imax format.

According to industry insiders, Nolan is one of a small group of directors with the clout to demand film recording rather than digital. Director Nolan used film and effects to give Interstellar a very earthy organic feel. That worked and scenes transitioned pretty well to the sublime of outer space. Interstellar now shares the theaters with another interesting movie with science fiction leanings. The Stephen Hawking biography, “The Theory of Everything” is getting very good reviews. They hold different ties to science and I suspect sci-fi lovers will be attracted to seeing both. With Interstellar, out just one full day and I ran into moviegoers that had already seen it more than once.

Where does Interstellar stand compared to Stanley Kubricks works? It doesn’t make that grade of science fiction that stands up as a century-class movie. However, Thorne’s and Nolan’s accounting of black holes and worm holes and the use of gravity is excellent. Instellar makes a 21st Century use of gravity in contrast to Gravity that was stuck in the 20th Century warning us to be careful where you park your space vehicle. In the end, Matthew McConaughey serves humanity well. Anne Hathaway plays a role not unlike Jody Foster in Contact – an intellectual but sympathetic female scientist.

Jessica Chastain playing the grown up daughter of McConaughey brings real angst and an edge to the movie; even Mackenzie Foy playing her part as a child. Call it the view ports for each character – they are short and narrow and Chastain uses hers very well. Matt Damon shows up in a modest but key role and does not disappoint. Nolan’s directing and filmography is impressive, not splashy but one is gripped by scenes. Filming in the small confines of spaceships and spacesuits is challenging and Nolan pulls it off very well. Don’t miss Interstellar in the theaters. It matches and exceeds the quality of several recent science fiction movies. Stepping back onto the street after the movie, the world seemed surprisingly comforting and I was glad to be back from the uncertain future Nolan created.

Where Have All the Pulsars Gone? The Mystery at the Center of Our Galaxy

The galactic core, observed using infrared light and X-ray light. Credit: NASA, ESA, SSC, CXC, and STScI

The galactic center is a happening place, with lots of gas, dust, stars, and surprising binary stars orbiting a supermassive black hole about three million times the size of our sun. With so many stars, astronomers estimate that there should be hundreds of dead ones. But to date, scientists have found only a single young pulsar at the galactic center where there should be as many as 50.

The question thus arises: where are all those rapidly spinning, dense stellar corpses known as pulsars? Joseph Bramante of Notre Dame University and astrophysicist Tim Linden of the University of Chicago have a possible solution to this missing-pulsar problem, which they describe in a paper accepted for publication in the journal Physical Review Letters.

Maybe those pulsars are absent because dark matter, which is plentiful in the galactic center, gloms onto the pulsars, accumulating until the pulsars become so dense they collapse into a black hole. Basically, they disappeared into the fabric of space and time by becoming so massive that they punched a hole right through it.

Dark matter, as you may know, is the theoretical mass that astrophysicists believe fills roughly a quarter of our universe. Alas, it is invisible and undetectable by conventional means, making its presence known only in how its gravitational pull interacts with other stellar objects.

One of the more popular candidates for dark matter is Weakly Interacting Massive Particles, otherwise known as WIMPs. Underground detectors are currently hunting for WIMPs and debate has raged over whether gamma rays streaming from the galactic center come from WIMPs annihilating one another.

In general, any particle and its antimatter partner will annihilate each other in a flurry of energy. But WIMPs don’t have an antimatter counterpart. Instead, they’re thought to be their own antiparticles, meaning that one WIMP can annihilate another.

But over the last few years, physicists have considered another class of dark matter called asymmetric dark matter. Unlike WIMPs, this type of dark matter does have an antimatter counterpart.

Numerical simulation of the density of matter when the universe was one billion years old. Cosmic Infrared Background ExpeRIment (CIBER) Credit: Caltech/Jamie Bock
 Cosmic Infrared Background ExpeRIment (CIBER) simulation of the density of matter when the universe was one billion years old, as produced by large-scale structures from dark matter. Credit: Caltech/Jamie Bock

Asymmetric dark matter appeals to physicists because it’s intrinsically linked to the imbalance of matter and antimatter. Basically, there’s a lot more matter in the universe than antimatter – which is good considering anything less than an imbalance would lead to our annihilation. Likewise, according to the theory, there’s much more dark matter than anti-dark-matter.

Physicists think that in the beginning, the Big Bang should’ve created as much matter as antimatter, but something altered this balance. No one’s sure what this mechanism was, but it might have triggered an imbalance in dark matter as well – hence it is “asymmetric”.

Dark matter is concentrated at the galactic center, and if it’s asymmetric, then it could collect at the center of pulsars, pulled in by their extremely strong gravity. Eventually, the pulsar would accumulate so much mass from dark matter that it would collapse into a black hole.

The idea that dark matter can cause pulsars to implode isn’t new.  But the new research is the first to apply this possibility to the missing-pulsar problem.

If the hypothesis is correct, then pulsars around the galactic center could only get so old before grabbing so much dark matter that they turn into black holes. Because the density of dark matter drops the farther you go from the center, the researchers predict that the maximum age of pulsars will increase with distance from the center. Observing this distinct pattern would be strong evidence that dark matter is not only causing pulsars to implode, but also that it’s asymmetric.

“The most exciting part about this is just from looking at pulsars, you can perhaps say what dark matter is made of,” Bramante said. Measuring this pattern would also help physicists narrow down the mass of the dark matter particle.

    Artist's illustration of a pulsar that was found to be an ultraluminous X-ray source. Credit: NASA, Caltech-JPL
Artist’s illustration of a pulsar that was found to be an ultraluminous X-ray source.
Credit: NASA, Caltech-JPL

But as Bramante admits, it won’t be easy to detect this signature. Astronomers will need to collect much more data about the galactic center’s pulsars by searching for radio signals, he claims. The hope is that as astronomers explore the galactic center with a wider range of radio frequencies, they will uncover more pulsars.

But of course, the idea that dark matter is behind the missing pulsar problem is still highly speculative, and the likelihood of it is being called into question.

“I think it’s unlikely—or at least it is too early to say anything definitive,” said Zurek, who was one of the first to revive the notion of asymmetric dark matter in 2009. The tricky part is being able to know for sure that any measurable pattern in the pulsar population is due to dark-matter-induced collapse and not something else.

Even if astronomers find this pulsar signature, it’s still far from being definitive evidence for asymmetric dark matter. As Kathryn Zurek of the Lawrence Berkeley National Laboratory explained: “Realistically, when dark matter is detected, we are going to need multiple, complementary probes to begin to be convinced that we have a handle on the theory of dark matter.”

And asymmetric dark matter may not have anything to do with the missing pulsar problem at all. The problem is relatively new, so astronomers may find more plausible, conventional explanations.

“I’d say give them some time and maybe they come up with some competing explanation that’s more fleshed out,” Bramante said.

Nevertheless, the idea is worth pursuing, says Haibo Yu of the University of California, Riverside. If anything, this analysis is a good example of how scientists can understand dark matter by exploring how it may influence astrophysical objects. “This tells us there are ways to explore dark matter that we’ve never thought of before,” he said. “We should have an open mind to see all possible effects that dark matter can have.”

There’s one other way to determine if dark matter can cause pulsars to implode: To catch them in the act. No one knows what a collapsing pulsar might look like. It might even blow up.

“While the idea of an explosion is really fun to think about, what would be even cooler is if it didn’t explode when it collapsed,” Bramante said. A pulsar emits a powerful beam of radiation, and as it spins, it appears to blink like a lighthouse with a frequency as high as several hundred times per second. As it implodes into a black hole, its gravity gets stronger, increasingly warping the surrounding space and time.

Studying this scenario would be a great way to test Einstein’s theory of general relativity, Bramante says. According to theory, the pulse rate would get slower and slower until the time between pulses becomes infinitely long. At that point, the pulses would stop entirely and the pulsar would be no more.

Further Reading: APS Physics, WIRED