The evidence for the existence of black holes


The evidence for the existence of black holes - Astronomers Are Getting Ready To Take The Image Of The Century And Here's What It Will Look Like  - NASA/CXC/M.Weiss An artist's drawing of a black hole named Cygnus X-1. It formed when a large star caved in. This black hole pulls matter from blue star beside it. Researchers studying the universe are ramping up to take the "image of the century" — the first image of a supermassive black hole. 

Since the 18th century, astronomers have discussed the possibility of exotic objects in space so massive that their gravitational grip swallows everything that dares to get too close, including light. We call these objects black holes, but in truth we do not know what a black hole really is because we've never actually seen one. 

The evidence for the existence of black holes, however, is compelling: 


"We have abundant evidence that black holes — or something very much like them — exist," Todd Thompson, astronomy professor at Ohio State University, told Business Insider earlier this year. "This evidence comes from the orbits of stars around the supermassive black hole at the center of our galaxy." 

Scientists will continue to argue the contrary until physical, observational evidence is provided. 

Now, a dedicated team of astrophysicists armed with a global fleet of powerful telescopes is out to change that. If they succeed, they will snap the first picture of the monstrously massive black hole thought to live at the center of our home galaxy, the Milky Way. 

It will be the "image of the century" according to scientists at the MIT Haystack Observatory, one of the 13 institutes from around the world involved with the project. 

This ambitious project, called the Event Horizon Telescope (EHT), is incredibly tricky, but recent advances in their research are encouraging the team to push forward. 

EHT needs to be so complex because black holes by definition do not emit light, making them invisible. In fact, black holes survive by gobbling up light and any other matter — nearby dust, gas, and stars — that fall into their powerful clutches. How To Glimpse A Black Hole 

So, how do you see something that is invisible? The answer leads us to the most advanced sub-millimeter telescopes in use — telescopes that detect wavelengths of light longer than the human eye can see. 

The EHT team is going to zoom in on a miniscule spot on the sky toward the center of the Milky Way where they believe to be the event horizon of a supermassive black hole weighing in at 4 million times the mass of our sun. 

Every black hole has a point of no return, called the event horizon. Once light, or anything else in the universe, passes the event horizon, it never escapes and is swallowed up. Forever. 

We can still see the material, however, right before it falls into eternal darkness. The EHT team is going to try to glimpse this ring of radiation that outlines the event horizon. Experts call this outline the "shadow" of a black hole, and it's this shadow that the EHT team is ultimately after to prove the existence of black holes. 

Below is a perfectly clear computer-generated image on the left of what scientists think the shadow will look like, and on the right is what they expect to actually see with the resolving power of today's current technology. 

 
Courtesy of Sheperd Doeleman. 

"If we see the shadow, that will be the most powerful evidence we have" that black holes exist, MIT's Shep Doeleman told PBS. A Difficult Task 

This shadow, however, is incredibly small from our perspective. 

The spot on the sky where the team is looking is the size a grapefruit would appear on the moon, as seen from Earth. The Hubble Space Telescope couldn't even see something this small. 

That's why the EHT team turned to radio dish telescopes in Hawaii, Arizona, California, Chile, and Spain that, when combined, can resolve details more than 2,000 times finer than Hubble. 

Recently, other EHT researchers, at the University of Arizona, simulated what our galaxy's central black hole and its shadow should look like, to get a better idea of what they might expect from their observations. 

"That ring of light makes the black hole easier to find than if we were looking for complete blackness," Dimitrios Psaltis, of The University Of Arizona, said in a statement. "These simulations also help us find ways to distinguish this signature from all this swirling plasma around the black hole." 

As shown in the clip below, the black hole at our galaxy's center is emitting jets of extremely hot plasma in confined columns at opposite ends. These columns are known as jets and have been observed around other objects throughout the universe. The EHT team wants to see beyond these jets, to the event horizon. 

Using the university's powerful supercomputer, they created a black hole that is even more scientifically accurate than the visually stunning black hole in Christopher Nolan's latest film, "Interstellar." 

"Our team of four here at the UA can produce visuals of a black hole that are more scientifically accurate in a few seconds," Feryal Ozel, also of The University of Arizona, in the statement. Some of the visuals in "Interstellar" required a special-effects team of 30 and as many as 100 hours for the computers to process. Building The Telescope Team 

To further improve its chances of seeing a black hole's shadow, the EHT team is continuously adding new telescopes to their global network. This is because the sensitivity of their measurements increases with each additional telescope, allowing the team to measure finer and finer detail. 

The Atacama Large Millimeter/submillimeter Array (ALMA) — the world's most powerful submillimeter array — is slated to join the EHT project soon, along with additional telescopes in Mexico and the South Pole. 

Last July, scientists installed the world's most precise atomic clock, costing $250,000, at ALMA's Operations base. The clock will sync ALMA's telescopes to other observatories of the EHT to ensure their recordings are accurate to within milliseconds. In fact, this atomic clock is so precise it will still be accurate to within a second 100 million years from now. 

ALMA will drastically improve EHT's resolving power: 

"At a single stroke, it increases the collecting area of the global array by nearly a factor of 10," Doeleman told Business Insider in an email. "[It] forms critical baselines (inter-antenna connections) that are essential fo creating good images of the event horizon." 

Below is an computer-generated image comparing how the shadow of a black hole in another galaxy, called M87, appears with and without ALMA (and other telescopes that make up the full EHT array.) 

 
Courtesy of Sheperd Doeleman. "The Event Horizon Telescope is the first to resolve spatial scales comparable to the size of the event horizon of a black hole," University of California Berkeley astronomer Jason Dexter told Universe Today . "I don't think it's crazy to think we might get an image in the next five years."

This article originally appeared in : Astronomers Are Getting Ready To Take The Image Of The Century And Here's What It Will Look Like | businessinsider.co.id | By Jessica Orwig | Mon, Dec 8, 2014, 7:05 AM EST




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