Archive for January, 2012

Reader mail: How far do black hole bullets blast out into space?

January 30, 2012 Leave a comment

As I reported on January 10, on or about June 3, 2009, enormous blobs of hot electrically charged matter were ejected from a black hole at about a quarter of the speed of light — roughly 75 million meters per second. Astronomers used a globe-spanning network of telescopes to observe the event, which occurred in a star system called H1743–322, about 28,000 light-years from Earth. A team of scientists reported the observations at the most recent meeting of the American Astronomical Society in Austin, Texas.

Geeked On Goddard reader John Conway contacted us with this excellent question:

“Interesting article. My thought: Do these “bullets” of gas dissipate over distance traveled, or do they keep going into space? If they were to come into contact with another celestial body, star, planet, black hole, whatever, what might be the result?”

I asked one of the astronomers who observed the goings-on at the black hole, James Miller-Jones, to explain.

“As the bullets move away from the black hole, they expand gradually,” Miller-Jones said. “Think of a bullet of material moving down a cone, whose apex is at the black hole.  If you take a slice through the cone to get a circular cross-section, that cross section gets bigger as you move away from the black hole. In the same way, the bullets are expanding as they move outwards.

“However, just because the bullets are too faint to detect doesn’t mean they have dissipated. They keep moving outwards, sweeping up or pushing aside the rarefied interstellar gas that is in the path of the bullets.Once they have swept up an amount of gas with a rest mass energy equal to their own initial energy (kinetic plus rest mass energy), they will slow down.”

And what would happen to a planet or star that got in the path of the bullets? Miller-Jones says it depends how close the object lies. In a binary star system (like H1743–322), the black holes co-orbits a nearby companion star, sucking gas off its surface. If the black-hole bullets hit the nearby star, “they would be expected to blast material off the surface of the donor.”

For more distant objects, the effect of the impact would be correspondingly less.

Then I asked Miller-Jones to estimate how far the bullets travel, and how fast. For example, if a black hole were located at the center of our solar system, how far outward would the bullets travel? Beyond Pluto? Beyond the distant shell of comets (the Kuiper belt) encircling the solar system? Or beyond the boundaries of the solar system to the vast space between our sun and the next star?

“We tracked these bullets way beyond [the distance from our sun to Pluto], and even beyond the Kuiper belt. Our last measurement put them about 120 times the sun-Earth distance from the black hole (120 astronomical units, or AU), whereas the Kuiper belt goes out to about 55 AU.

“In terms of how far the bullets travel before we can no longer detect them, that depends very much on the opening angle of the cone (how “wide” or “narrow” it is), the original energy of the outburst, and on how far away the source was.  With our most sensitive telescopes, and with the brightest bullets from the brightest black hole outbursts, we’ve tracked them out to about 0.1-0.2 light years from the black hole.  But we have no reason to think that they stopped there.”

Miller-Jones said that a blast of black-hole bullets would quickly leave the boundaries of its home solar system and enter interstellar space. For something like the bullets he and his colleagues studied, it would take them just a few days to exit a solar system about the size of ours, moving at about 25 percent of the speed of light.

Thanks to John Conway for his great questions.

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.



Why did a black hole blast star stuff into space at a quarter of light-speed on June 3, 2009? Here is what happened

January 10, 2012 3 comments

On June 3, 2009, in an X-ray binary star system far, far away. . .

We know the what of the extraordinary event that occurred in May 2009 around a distant black hole; we just don’t know the why of it, although the possibilities are pretty amazing.

At the 2012 American Astronomical Society (AAS) meeting in Austin, Texas, Gregory Sivakoff of the University of Alberta in Canada reported some astounding observations he and his colleagues accomplished using a globe-spanning array of radio telescopes and two NASA satellites.

The whole episode was a cosmic stroke of luck: The light from an event that happened some 28,000 years ago reached Earth just days before the global collaboration was scheduled to open for business. Goddard astrophysics writer Francis Reddy explains the details of the science today in a web feature story and animation.

Let’s start with the what: On or about June 3, 2009, enormous blobs of hot electrically charged matter were ejected from a black hole at about a quarter of the speed of light — roughly 75 million meters per second.

Next, the where: These black-hole “bullets,” as Reddy calls them in his web feature, were ejected from a binary star system. Called H1743–322, the  system lies about 28,000 light-years from Earth. NASA’s HEAO-1 satellite discovered it in 1977

In H1743–322, a black hole and a star orbit each other at close quarters, every few days. They are close enough that the black hole’s massive gravity draws a steady stream of material off its companion’s wispy surface. The hot electrically charged gas swirls around the edge of the black hole, forming a whirlpool-like “accretion disc.” As the gas accelerates to high speed, it radiates X-rays that satellites at Earth can detect.

“Some of the infalling matter becomes re-directed out of the accretion disk as dual, oppositely directed jets,” Reddy writes. “Most of the time, the jets consist of a steady flow of particles. Occasionally, though, they morph into more powerful outflows that hurl massive gas blobs at significant fractions of the speed of light.”

Years ago, Sivakoff’s colleague James Miller-Jones, currently based at the International Center for Radio Astronomy Research at Curtin University in Perth, Australia, conceived of a plan to mount a “multiwavelength campaign” to study the periodic outbursts that astronomers observe from X-ray binaries like H1743–322. They got their chance on May 22, 2009.

On that date, renewed activity around the black hole triggered the Burst Alert Telescope on NASA’s Swift satellite. Miller-Jones, Sivakoff, and the other members of the international team of observers were able to marshal three radio telescopes: the Very Long Baseline Array, the Very Large Array, and the Australia Telescope Compact Array. The team also drew on data from NASA’s Rossi X-ray Timing Explorer (RXTE) satellite (which was just switched off this week, by the way, after 16 years of meritorious service).

Using information from the telescopes and satellites, the scientists were able to reconstruct the events leading up to and following the ejection of black-hole bullets from the binary system. Sivakoff reported those findings today at the AAS meeting.

Now, finally, what about the “how” of this outburst? That’s not very clear yet.

In similar black hole binaries, Miller-Jones says, astronomers have measured ejections traveling 92 percent of the speed of light!  What process can shoot giant blobs of stuff out of the accretion zone of a black hole at such incredible speeds?

Sivakoff sketches out one possible explanation: Imagine knots of mass in the accretion disc, swirling around, getting closer and closer to the black hole. The disc is looped by powerful magnetic fields, which twist and tangle together as the disc rotates. When magnetic flux lines cross and connect, it could release enough energy to boost the black-hole bullets up and out of the disk.

“I think of a fairly stiff rope that is firmly to attached to the accretion disc,” Sivakoff explains. “As the disc spins, the rope is wound up, forming a sort of helix. Of course, there’s not one but many such ropes in an accretion disc. If two of those ropes touch — what astronomers call magnetic reconnection — lots of energy can be released. I like to envision ‘crossing the streams,’ a la Ghost Busters. This energy can accelerate particles, launching the bullet.”

There is another scenario, Miller-Jones says. Some scientists have proposed that what actually happens is that the inner edge of the accretion disc constricts, edging closer to the black hole’s “event horizon,” beyond which matter cannot escape. The magnetic and gravitational forces at this border region are extremely intense.

The forces could unleash a surge of material into the black hole’s paired jets, with a wavelike shock front ahead of it. “This causes particle acceleration,” Miller-Jones says, “and hence bright radio emission at this shock front.” So the bullets may actually be sudden surges in the jets, not discrete blobs.

But these explanations are just informed speculation at the moment. Additional multi-telescope observations could eventually provide enough clues to untangle the extreme physics that power black-hole bullets.

The team can only hope their recent stroke of luck holds out. Sivakoff says that the H1743–322  system conveniently started to flare up in late May 2009 — just as the team was preparing for the official opening of their observing window.

“Technically our observing was supposed to start in June 2009,” Sivakoff says. “But when this outburst went off a few days before our window was supposed to open up, we actually got permission to start observing earlier.”

So the discovery was the team’s inaugural run. “This was quite a trial by fire,” Sivakoff says.

OH AND DID I MENTION? All opinions and opinionlike objects in this blog are mine alone and NOT those of NASA or Goddard Space Flight Center. And while we’re at it, links to websites posted on this blog do not imply endorsement of those websites by NASA.

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