On April 10, scientists released the first visual evidence of a supermassive black hole. The image, a result of international collaboration between scientists and eight separate telescopes collectively known as the Event Horizon Telescope, shows a blurry orange ring and—that’s all. “Sometimes seeing is believing but in this case not seeing is believing,” says professor of physics and dean emeritus Tom Helliwell. Of course, the dark space inside the orange ring is the black hole, which lurks some 55 million light-years away from Earth in the M87 galaxy. “The bright ring around the black hole is emitted by the matter orbiting the black hole, gradually drifting inward as it orbits, until it approaches the event horizon and subsequently vanishes from our view,” Helliwell says. “Evidence for black holes has been very strong for a long time now,” Helliwell says. “The picture is a graphical confirmation that black holes really do exist in the nuclei of galaxies. The first-ever picture of a black hole is very impressive. Einstein would have been amazed!”
So, what’s so amazing about it? We surveyed Helliwell and other members of the Harvey Mudd physics community to find out.
“There are a lot of scientific reasons to be excited about the discovery, but in some ways, I think the biggest impact for the general public is the visceral nature of the images: that we can actually see the black hole as a hole in the Event Horizon Telescope image,” says physics professor Brian Shuve. Until now, he says, “evidence has always been in a slightly more abstract form—we see them by the very high energy particles that are ejected in the vicinity of the black hole, but we don’t actually see the hole itself. So it’s exciting because we can see black holes in a real, tangible way that we haven’t been able to before.”
Physics professor Vatche Sahakian says that because black holes are the most extreme physical phenomena in the universe, “they test the limits of our understanding of fundamental physics. Hence, any observational insight into black holes and data about how they function is bound to have profound impact on science—from relativity to gravitational physics to even quantum mechanics. The recent imaging of the first black hole constitutes a test of Einstein’s theory of general relativity in the strong gravity regime, a realm put to test only one other time— through the detections of gravitational waves from spiraling black holes and neutron stars. This observation is a breakthrough as it constitutes a direct observation and a proof of concept for imaging these extreme objects. As image resolution undoubtedly improves in the near future, we should expect many more ground-breaking results and the onset of a new area of observational astrophysics with all the surprises it might hold.”
Shuve agrees. “This allows us to test the theory of general relativity with great precision in an environment where we expect gravitational effects to be at their most important. Most other ways we have tested general relativity is via relatively subtle effects, and so it could be that our theory is incomplete and we just haven’t been able to see it yet. Imaging black holes allows us to see how well our theory is working at describing the physics of black holes.”
In addition to the potential for improved study of general relativity, UC Davis physics professor Andrew Wetzel ’05 believes imaging the black hole will answer questions about how galaxies form. “This particular black hole, in the center of galaxy M87, is particularly supermassive, about 6.5 billion times the mass of the Sun, or more than 1,000 times the mass of the supermassive black hole at the center of our own Milky Way galaxy,” he says. “We now think that these supermassive black holes have strong influence on the whole galaxy itself: The relativistic jets and hot gas near the black hole can have violent consequences on gas throughout the galaxy. So our better understanding of this black hole helps our understanding of how galaxies like M87 formed as well.”
Helliwell is interested to see the discoveries that will be made as scientists will “undoubtedly peer into the hearts of other many other galaxies as well, including the nucleus of our own Milky Way galaxy, where dwells a smaller but still substantial black hole of four million solar masses.”
He’s also excited about the black hole image for more terrestrial reasons. “It is equally impressive to me that the picture required the use of eight radio telescopes scattered around the globe, in a truly international collaboration,” Helliwell says. “No single country could have done it! It seems that it will often take the same kind of international effort to make some other scientific discoveries and to solve such critical global problems as climate change, human migration and extreme poverty. Maybe scientific collaborations can serve as models for how to tackle these humanitarian problems as well.”