Black hole, star collisions may illuminate universe's dark side

Sep 19, 2011
Princeton and New York University researchers have simulated the effect of a primordial black hole passing through a star. Primordial black holes are among the objects hypothesized to make up dark matter -- the invisible substance thought to constitute much of the universe -- and astronomers could use the researchers' model to finally observe the elusive black holes. This image illustrates the resulting vibration waves as a primordial black hole (white dots) passes through the center of a star. The different colors correspond to the density of the primordial black hole and strength of the vibration. Credit: Image by Tim Sandstrom

Scientists looking to capture evidence of dark matter -- the invisible substance thought to constitute much of the universe -- may find a helpful tool in the recent work of researchers from Princeton University and New York University.

The team unveiled in a report in the journal this month a ready-made method for detecting the collision of with an elusive type of black hole that is on the short list of objects believed to make up dark matter. Such a discovery could serve as observable proof of dark matter and provide a much deeper understanding of the universe's inner workings.

Postdoctoral researchers Shravan Hanasoge of Princeton's Department of and Michael Kesden of NYU's Center for Cosmology and simulated the visible result of a primordial black hole passing through a star. Theoretical remnants of the Big Bang, primordial black holes possess the properties of dark matter and are one of various cosmic objects thought to be the source of the mysterious substance, but they have yet to be observed.

If primordial black holes are the source of dark matter, the sheer number of stars in the -- roughly 100 billion -- makes an encounter inevitable, the authors report. Unlike larger black holes, a primordial black hole would not "swallow" the star, but cause noticeable vibrations on the star's surface as it passes through.

Thus, as the number of telescopes and satellites probing in the Milky Way increases, so do the chances to observe a primordial black hole as it slides harmlessly through one of the galaxy's billions of stars, Hanasoge said. The developed by Hanasoge and Kesden can be used with these current solar-observation techniques to offer a more precise method for detecting primordial black holes than existing tools.

"If astronomers were just looking at the sun, the chances of observing a primordial black hole are not likely, but people are now looking at thousands of stars," Hanasoge said.

"There's a larger question of what constitutes dark matter, and if a primordial black hole were found it would fit all the parameters -- they have mass and force so they directly influence other objects in the universe, and they don't interact with light. Identifying one would have profound implications for our understanding of the early universe and dark matter."

Although dark matter has not been observed directly, galaxies are thought to reside in extended dark-matter halos based on documented gravitational effects of these halos on galaxies' visible stars and gas. Like other proposed dark-matter candidates, primordial black holes are difficult to detect because they neither emit nor absorb light, stealthily traversing the universe with only subtle gravitational effects on nearby objects.

Because primordial black holes are heavier than other dark-matter candidates, however, their interaction with stars would be detectable by existing and future stellar observatories, Kesden said. When crossing paths with a star, a primordial black hole's gravity would squeeze the star, and then, once the black hole passed through, cause the star's surface to ripple as it snaps back into place.

"If you imagine poking a water balloon and watching the water ripple inside, that's similar to how a star's surface appears," Kesden said. "By looking at how a star's surface moves, you can figure out what's going on inside. If a black hole goes through, you can see the surface vibrate."

Eyeing the sun's surface for hints of dark matter

Kesden and Hanasoge used the sun as a model to calculate the effect of a primordial black hole on a star's surface. Kesden, whose research includes black holes and dark matter, calculated the masses of a primordial black hole, as well as the likely trajectory of the object through the sun. Hanasoge, who studies seismology in the sun, Earth and stars, worked out the black hole's vibrational effect on the sun's surface.

Video simulations of the researchers' calculations were created by NASA's Tim Sandstrom using the Pleiades supercomputer at the agency's Ames Research Center in California. One clip shows the vibrations of the sun's surface as a primordial black hole -- represented by a white trail -- passes through its interior. A second movie portrays the result of a black hole grazing the Sun's surface.

Marc Kamionkowski, a professor of physics and astronomy at Johns Hopkins University, said that the work serves as a toolkit for detecting primordial black holes, as Hanasoge and Kesden have provided a thorough and accurate method that takes advantage of existing solar observations. A theoretical physicist well known for his work with large-scale structures and the universe's early history, Kamionkowski had no role in the project, but is familiar with it.

"It's been known that as a primordial black hole went by a star, it would have an effect, but this is the first time we have calculations that are numerically precise," Kamionkowski said.

"This is a clever idea that takes advantage of observations and measurements already made by solar physics. It's like someone calling you to say there might be a million dollars under your front doormat. If it turns out to not be true, it cost you nothing to look. In this case, there might be in the data sets astronomers already have, so why not look?"

One significant aspect of Kesden and Hanasoge's technique, Kamionkowski said, is that it narrows a significant gap in the mass that can be detected by existing methods of trolling for primordial black holes.

The search for primordial black holes has thus far been limited to masses too small to include a black hole, or so large that "those black holes would have disrupted galaxies in heinous ways we would have noticed," Kamionkowski said. "Primordial black holes have been somewhat neglected and I think that's because there has not been a single, well-motivated idea of how to find them within the range in which they could likely exist."

The current mass range in which primordial black holes could be observed was set based on previous direct observations of Hawking radiation -- the emissions from black holes as they evaporate into gamma rays -- as well as of the bending of light around large stellar objects, Kesden said. The difference in mass between those phenomena, however, is enormous, even in astronomical terms. Hawking radiation can only be observed if the evaporating black hole's mass is less than 100 quadrillion grams. On the other end, an object must be larger than 100 septillion (24 zeroes) grams for light to visibly bend around it. The search for primordial black holes covered a swath of mass that spans a factor of 1 billion, Kesden explained -- similar to searching for an unknown object with a weight somewhere between that of a penny and a mining dump truck.

He and Hanasoge suggest a technique to give that range a much-needed trim and established more specific parameters for spotting a primordial black hole. The pair found through their simulations that a primordial black hole larger than 1 sextillion (21 zeroes) grams -- roughly the mass of an asteroid -- would produce a noticeable effect on a star's surface.

"Now that we know primordial can produce detectable vibrations in stars, we could try to look at a larger sample of stars than just our own sun," Kesden said.

"The Milky Way has 100 billion stars, so about 10,000 detectable events should be happening every year in our galaxy if we just knew where to look."

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SpiffyKavu
3 / 5 (2) Sep 19, 2011
Should the last sentence of the image caption read: "The different colors correspond to the density of the [distripted] star..." As opposed to the "primordial black hole"?
ubavontuba
2 / 5 (7) Sep 19, 2011
Cool concept.

If this pans out, it'll certainly mean the demise of the Hawking radiation hypothesis though (Contray to the article's contention, it has never been observed).

I wonder how massive the black hole would have to be, to be detectable in a star (pretty massive, I'm guessing).

Could this be scaled down to measure micro black holes passing through highly compressed liquids and/or gasses?

ubavontuba
1 / 5 (2) Sep 19, 2011
Ah, I found it: "1 sextillion grams" That's remarkably small. It's schwarzschild diameter would be about the size of a smallish molecule (I think).

yyz
4.5 / 5 (8) Sep 19, 2011
"The pair found through their simulations that a primordial black hole larger than 1 sextillion (21 zeroes) grams -- roughly the mass of an asteroid -- would produce a noticeable effect on a star's surface."

"...we know primordial black holes can produce detectable vibrations in stars..."

That being the case, why again does helioseismology fail to detect omatumr's solar-mass neutron star within the Sun OR "a mantle made mostly of Fe, O, Ni, Si, S, Mg and Ca"?

______________________________________


As to the article, certainly an interesting proposition these authors put forward. Their paper can be found here: http://arxiv.org/...11v1.pdf

ubavontuba
1.8 / 5 (5) Sep 19, 2011
Ooh! I just did the calculation. I get 1.4849427648091593nm. Is that correct? That's just a tad bigger than a carbon atom!

ubavontuba
2.7 / 5 (7) Sep 19, 2011
That being the case, why again does helioseismology fail to detect omatumr's solar-mass neutron star within the Sun OR "a mantle made mostly of Fe, O, Ni, Si, S, Mg and Ca"?


"Helioseismology was able to rule out the possibility that the solar neutrino problem was due to incorrect models of the interior of the Sun."

http://en.wikiped...ismology

But I do now wonder how big he thinks this supposed core is. Perhaps he feels it's small enough to avoid detection by this method?

Decimatus
2.8 / 5 (4) Sep 19, 2011
Guys, look at that picture.... there is a neutron star in the core! Oliver was right!

On a more serious note, how likely is it that a primordial blackhole just zips through a star without getting trapped? What would the velocity have to be for a sun mass star?

Seems to me like you would detect an oddly exploding star with a blackhole remnant, not some faint vibrations on the surface.
Decimatus
1 / 5 (2) Sep 19, 2011
In fact, if that were the case, then I would think that you could potentially have some leftover blackhole that fall wildly under the mass limit for such supernova.

Assuming of course that a star capturing a tiny blackhole would explode, but I don't see what eslece could happen with such a disruptive force taking up residence in a star.

A question might be of time. If a 1 atom wide blackhole sat in the sun's core, how long would it take before it could absorb enough matter to be a factor? Given that it might rely mostly on collision, I can see the process taking quite a long time.

Maybe most if not all stars are just ticking time bombs, waiting for their primordial blackholes to gain enough mass to become a threat to star stability?

Crazy but interesting.
ekim
not rated yet Sep 19, 2011
Why are these measurements in grams and not tonnes?
Pyle
5 / 5 (1) Sep 19, 2011
ekim, because as uba said "That's just a tad bigger than a carbon atom!"
@uba:
If this pans out, it'll certainly mean the demise of the Hawking radiation hypothesis though
How long should it have taken for primordial BH's to evaporate via Hawking radiation? Couldn't the reduced surface area and the relative size in relation to the plank width potentially make evaporation take a very very long time, on average? (I actually don't like the primordial BH theory, but thought I'd ask for your thoughts for fun since I am too lazy to do any research today.)
ubavontuba
2.7 / 5 (7) Sep 20, 2011
Guys, look at that picture.... there is a neutron star in the core! Oliver was right!
LOL. It does look like there's a nondescript blob in the center, doesn't it?

how likely is it that a primordial blackhole just zips through a star without getting trapped?
Extremely likely.

What would the velocity have to be for a sun mass star?
Just above escape velocity. And ostensibly, having not originated as part of the solar system, it's inherently well above escape velocity to begin with.
ubavontuba
2.6 / 5 (5) Sep 20, 2011
@Pyle:

How long should it have taken for primordial BH's to evaporate via Hawking radiation?
It depends on their initial mass. Primordial Black holes (PBH) with masses around 10^15 grams are supposed to be fizzling out today. Anything above that is still supposedly around, and anything below that is supposedly already gone. Of course this is much smaller than the mass discussed in the article, but if such tiny PBH's as in the article are common, you might reasonably expect even smaller sizes to likewise be common. And since we haven't detected any evaporation signals (they should be everywhere, if they make up dark matter), either they don't evaporate, don't exist, or their original size was inexplicably constrained above certain limitations.

Couldn't the reduced surface area and the relative size in relation to the plank width potentially make evaporation take a very very long time, on average?
The smaller they are, the faster they supposedly evaporate.

contd...
ubavontuba
2.3 / 5 (6) Sep 20, 2011
(I actually don't like the primordial BH theory,
I do. I think it's the simplest and least mysterious explanation for dark matter (and perhaps dark energy). But it works for me because I'm not a big fan of the Hawking radiation hypothesis (as you undoubtedly know).

but thought I'd ask for your thoughts for fun since I am too lazy to do any research today.)
LOL! I'm only writing in the forum today, 'cause I'm feeling too lazy to do any real work myself! LOL!