Did 'Interstellar' get it right?
The world will finally get to see how a black hole looks like.
The first-ever close-up of a black hole — the spaces at the center of every large galaxy — can be seen by the public at 9pm Beijing time today when six simultaneous press conferences are held in Shanghai, Taipei, Brussels, Chile’s Santiago, Tokyo and Washington.
The picture will have been captured by the Event Horizon Telescope, a network of eight radio telescopes scattered across the globe, thus creating a giant virtual telescope with a diameter equaling that of the Earth.
The EHT allows astronomers to clearly see an orange on the Moon.
The project’s researchers obtained the first data in April 2017 from the global network of telescopes.
The telescopes that collected that initial data are located in the US states of Arizona and Hawaii as well as Mexico, Chile, Spain and Antarctica. Since then, telescopes in France and Greenland have been added to the network.
The telescopes were trained on two supermassive black holes in very different corners of the universe to collect data. Sagittarius A*, in a mass of 4 million suns, is located at the center of the Milky Way, and another, unnamed, is located at the center of the neighboring Virgo A galaxy, weighing 1,500 times of Sagittarius A*.
The picture to be unveiled today is likely to zoom in on one or the other. The data collected by the far-flung telescope array still had to be collected and collated.
“The imaging algorithms we developed fill the gaps of data we are missing in order to reconstruct a picture of a black hole,” the team said on its website.
The EHT project involves more than 200 astronomers from across the world, including those from China.
The research will put to the test a scientific pillar — physicist Albert Einstein’s theory of general relativity, according to University of Arizona astrophysicist Dimitrios Psaltis, project scientist for the EHT. That theory, put forward in 1915, was intended to explain the laws of gravity and their relation to other natural forces.
Black holes live up to their name. Basically, it is a place in space that swallows almost everything.
A black hole’s event horizon, one of the most violent places in the universe, is the point of no return beyond which anything — stars, planets, gas, dust, all forms of electromagnetic radiation including light — gets sucked in irretrievably.
For us, black holes are “dark stars.” So how do astronomers find black holes?
When black holes tear up nearby stars and swallow things in the space, they will emit great energy, generating bright light and massive radiation, through collision and friction.
That lead astronomers to the locations of black holes.
How do black holes look like?
No one knows, at least not until we discover it today.
Over the years, they have been depicted in many ways in the movies, but it is widely regarded that its image in the hit Hollywood movie “Interstellar” is the closest to the real thing.
Similar to the shape of Saturn, a star with rings, the black hole as depicted in “Interstellar” is very massive and rapidly spinning black with a glowing ring of matter encircling it.
The image was created after consultations with physicist and Nobel Laureate Kip Thorne of the California Institute of Technology.
Einstein’s theory, if correct, should allow for an extremely accurate prediction of the size and shape of a black hole.
“The shape of the shadow will be almost a perfect circle in Einstein’s theory,” Psaltis said. “If we find it to be different than what the theory predicts, then we go back to square one and we say, ‘Clearly, something is not exactly right.’”
Breakthrough observations in 2015 that earned the scientists involved a Nobel Prize used gravitational wave detectors to track two black holes smashing together.
As they merged, ripples in the curvatures of time-space created a unique, and detectable, signature.
“Einstein’s theory of general relativity says that this is exactly what should happen,” said Paul McNamara, an astrophysicist at the European Space Agency and an expert on black holes.
But those were tiny black holes — only 60 times more massive than the Sun — compared with either of the ones under the gaze of the EHT.
“Maybe the ones that are millions of times more massive are different — we just don’t know yet,” said McNamara.
How big is a black hole?
The diameter of a black hole depends on its mass but it is always double what we call the Schwarzschild radius. If the sun were to shrink to a singularity point, the Schwarzschild radius would be 3 kilometers and the diameter would be 6. For Earth, the diameter would be 18 millimeters, or about three quarters of an inch. The event horizon of the black hole at the center of the Milky Way, Sagittarius A*, measures about 24 million kilometers across.
What will the image look like?
The Event Horizon Telescope is not looking at the black hole per se, but the material it has captured. It won’t be a big disk in high resolution like in the Hollywood movie “Interstellar.” But we might see a black core with a bright ring — the accretion disk — around it. The light from behind the black hole gets bent like a lens. No matter what the orientation of the disk, you will see it as a ring because of the black hole’s strong gravity. Visually, it will look very much like an eclipse.
How is the image generated?
Rather than having one telescope that is 100 meters across, they have lots of telescopes with an effective diameter of 12,000km — the diameter of Earth. The data is recorded with very high accuracy, put onto hard disks, and shipped to a central location where the image is reconstructed digitally. This is very, very long baseline interferometry — over the entire surface of the Earth.