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

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.

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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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