A super-powered radio
telescopes has turned the Earth into one giant eye --the Event Horizon
Telescope (EHT), a multinational effort involving more than 100
researchers--all pointing to Sagittarius A*—the supermassive black hole at the
center of our galaxy first forecast by Albert Einstein and his theory of
general relativity, and since then the subject of study by countless
theoretical physicists, among them the famous cosmic detective Stephen Hawking.
The EHT plan focuses on the
relatively small but "nearby" supermassive black hole at the center
of our Milky Way galaxy and the distant, but extremely massive, black hole at
the center of the galaxy M87, a supergiant elliptical galaxy in the
constellation Virgo shown below--the most massive black hole for which a
precise mass has been measured -6.6 billion solar masses.
Orbiting the galaxy is an
abnormally large population of about 12,000 globular clusters, compared to
150-200 globular clusters orbiting the Milky Way. The M87 black hole grew to
its massive size by merging with several other black holes.
"While the event
horizons of big supermassive black holes are relatively large (about the size
of a solar system) the EHT's two targets are still very, very far away"
says Adam Frank an astrophysicist at the University of Rochester and a leading
expert on the final stages of evolution for stars like the sun in his 13.7 Blog
on NPR.
"Imagine using a
telescope in New York City to make an image of a quarter in Los Angeles that
was so good you could read the text on its face," he writes. "That's
the challenge EHT scientists face in imaging a black hole. To overcome this
challenge, they are pushing their technology to new extremes."
When you point two
electronically linked telescopes at the same object, what you get, in essence,
is a bigger telescope. Combining the light from the telescopes is what's called
interferometry — and it's remarkable and complicated. There are radio
telescopes in Chile, Mexico, Spain and the South Pole that are all in on the
EHT project. The EHT uses these instruments, stretched across the globe, to get
the highest resolving power possible.
Harvard astronomer Dimitrios
Psaltis ahas been working on black holes as part of the massive Event Horizon
Telescope project that will capture the first-ever image of the massive dark
void at the center of the Milky Way, the one scientists think is sucking up any
matter or radiation that wanders too close to its event horizon, or point of no
return.
Psaltis, a lead scientist on
the Event Horizon Telescope (EHT) project, that includes his wife, former
Radcliffe fellow Feryal Özel, and a series of super-powered radio telescopes
scattered around the globe.
Their results could prove
that Einstein's theory—the notion that gravity is due to the curvature of the
continuum known as space-time—is exact. Or, perhaps, just a little bit off.
"What we are looking
for is not a description of gravity," he said, "but the description
that happens to be the one that describes our universe."
To make those calculations,
researchers will need to see what has thus far been invisible. But how exactly
do you capture the image of a spinning, giant black abyss? You don't, said
Psaltis. You take a picture of its shadow.
Swirling around Sagittarius A* are charged particles that have been ejected from the surface of nearby stars. Moving at supersonic speeds, those particles heat up millions of degrees to form a shining mass of plasma, or "accretion disk," around the edge of the black hole before they are engulfed.
"The plasma is so hot
that it is actually glowing in the radio waves detected by the
telescopes," said Psaltis. "You put a black hole in front of that
glowing plasma and you get a shadow, you get a silhouette."
But, as the special effects
team for the movie "Interstellar" discovered, producing a realistic
image of a black hole is hugely time-consuming. (Some individual frames of the
film reportedly took 100 hours to render.)
Eager to accelerate the
process, Psaltis and his team hacked into their computer's graphics card, the
circuit board that controls how images appear on the screen, and gave it a
little something extra.
"We made it program
those chips to do the rendering in the presence of a black hole. … Our codes
are so fast that now we use a type of Xbox to control the process with our
hands because there's no way to type fast enough to do it."
If the image Psaltis and his
colleagues produce is perfectly round, it will indicate Einstein was entirely
correct.
But if the image starts to
warp and bend, it means his theory might need some tweaking.
"That nice circle that
you see here has a particular size, has a particular shape only because
Einstein's theory told us so," said Psaltis, pointing to a simulation on
his screen. "If the theory is different, both the size and the shape will
be different.
"The shape of the
shadow can be used to tell us exactly what that gravitational field looks like
outside that black hole," he added. "And by measuring that, either we
will be able to say if Einstein's theory predicts it 100 percent, or if there
are small tweaks that we need to add in order to get it right … this is the
smoking gun as far as Einstein's gravity is concerned."
Psaltis' current project has deep Harvard
roots. In the 1990s, he and Özel were both on campus, Psaltis doing
postdoctoral research, his future wife pursuing her Ph.D.
Together they collaborated
with Ramesh Narayan, the Thomas Dudley Cabot Professor of the Natural Sciences,
on early simulations that explored what happens to the plasma around a black
hole. That research helped determine that the radio wavelength that would give
them the best chance at seeing the black hole's event horizon was roughly one
millimeter long.
"We found that the plasma becomes more
and more transparent as you go to a higher and higher frequency and that's what
we calculated, where you need to make that observation in order to be able to
peer through the plasma," said Psaltis. At one millimeter you "see
the black hole's shadow," he said.
The work builds on research by Sheperd
Doeleman, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics
and principal investigator for the Event Horizon project. It was Doeleman who
first measured the size of the emitting region of the accretion disk, in 2008.
Skeptics persist. Despite its potential to
advance understanding of black holes and render a key scientific judgment on
Einstein's work, research like Psaltis' leaves some doubting an effect for life
on Earth when Sagittarius A* is 26,000 light-years away.
The native of Greece, who said he gets that
question "all the time," dons his philosopher's hat to answer it.
Such endeavors have a foot in both the past and future, he noted, and can also
illuminate specific events and ideas, from the Big Bang to investigations into
parallel universes.
Equally important is the notion that today's
research might have its greatest impact tomorrow, Psaltis said. To make his
case, he cited the work of the German mathematician Bernhard Riemann, who
challenged the accepted model of Euclidian geometry in the 1800s by imagining a
world in which two parallel lines ultimately crossed. Einstein would go on to
base general relativity on Riemann's mathematical framework.
"Not even in his wildest dreams could
Riemann have predicted that," said Psaltis. "But if he had not asked
in the 1800s, 'Is there any way to make two parallel lines cross?' we would not
have Einstein's theories, or GPS, since your phone makes calculations based on
Einstein's theories to determine where you are.
"Abstract thought is
good for intellectual curiosity," he added. "You never can tell where
that can take you."
So how close are we to seeing a black hole?
Remarkably close, say Adam Frank: "The EHT team is in the process of
analyzing data taken earlier this year. Given the complexity of joining
observations from so many telescopes, it likely will not be until December that
they know what they have."
Via DailyGalaxy.com