伊朗电视台日前发布新闻说
黑洞的能量效率惊人，如果地球上的汽车引擎效率能像黑洞一般，则一加仑的汽油可跑十亿英哩！
Waste not.
Surrounding matter is sucked toward a supermassive black hole, where
it is expelled back out at enormous speed in an incredibly efficient
process.
Credit: Harvard-Smithsonian Center for Astrophysics |
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High-Mileage Black Holes
By Phil Berardelli
ScienceNOW Daily News
24 April 2006
Astronomers have discovered that, deep inside the biggest and brightest galaxies
in the universe, jets are spewing particles from around black holes in an
incredibly energy-efficient manner. If an automobile engine worked as well as
one of these monsters, it could go more than a billion miles on a gallon of gas.
The surprise is these high-mileage black holes aren't quasars, which are
considered the most energetic and efficient bodies in the universe at converting
matter to energy . Instead, astronomers have discovered, they are relatively old
and quiet supermassive black holes that somehow can maintain similar
efficiencies while expelling much less energy.
The astronomers used data from the Chandra X-ray Observatory to study nine
supermassive black holes populating very large elliptical galaxies. In all
cases, they found the areas around the black holes to be dim in visible light
but quite bright in x-ray wavelengths. For the nine objects studied, they
calculated that the black holes could convert up to 2.5% of the infalling gas
and dust to energy--not quite as good as a quasar, which can average 5% or more,
but still about 25 times better than the best nuclear power reactors.
The team also found that the jets produced by the supermassives are streaming
outward at incredible speeds--in some cases 95% of the speed of light. "The
energy in these jets is absolutely huge," says lead researcher Steven Allen of
Stanford University in Palo Alto, California, "about a trillion, trillion,
trillion watts." The findings were announced during a media teleconference today
and will be published in an upcoming issue of the Monthly Notices of the
Royal Astronomical Society.
The question is what process converts the energy from the gas streaming in
toward the black holes to the enormous energy in the jets. So far, there is only
speculation, says co-author Christopher Reynolds of the University of Maryland,
College Park. One idea is that the rotational energy of the supermassives powers
the engine.
"We already knew quasars were enormously efficient at making light," says
Kimberly Weaver, an astrophysicist at NASA's Goddard Space Flight Center in
Greenbelt, Maryland. "Now we know black holes in elliptical galaxies are also as
efficient at making x-rays." This also could explain why there are few young
stars in these galaxies: When the jets collide with the surrounding interstellar
gas, they heat it to the point where it cannot condense into new stars.
"Just as with cars, it's critical to know the fuel efficiency of black
holes," Allen adds. "Without this information, we cannot figure out what is
going on under the hood, so to speak, or what the engine can do."
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