Astronomers Get Closest Look Yet At Milky Way's Mysterious Core

Nov 03, 2005
The Milky Way's nucleus, as seen with the VLA

Astronomers have gotten their deepest glimpse into the heart of our Milky Way Galaxy, peering closer to the supermassive black hole at the Galaxy's core then ever before.

Image: The Milky Way's nucleus, as seen with the VLA. Sagittarius A* is the bright
white dot at center. CREDIT: NRAO/AUI/NSF, Jun-Hui Zhao, W.M. Goss

Using the National Science Foundation's continent-wide Very Long Baseline Array (VLBA), they found that a radio-wave-emitting object at the Galaxy's center would nearly fit between the Earth and the Sun. This is half the size measured in any previous observation.

"We're getting tantalizingly close to being able to see an unmistakable signature that would provide the first concrete proof of a supermassive black hole at a galaxy's center," said Zhi-Qiang Shen, of the Shanghai Astronomical Observatory. A black hole is a concentration of mass so dense that not even light can escape its powerful gravitational pull.

The astronomers used the VLBA to measure the size of an object called Sagittarius A* (pronounced "A-star") that marks the exact center of our Galaxy. Last year, a different team announced that their measurements showed the object would fit inside the complete circle of Earth's orbit around the Sun. Shen and his team, by observing at a higher radio frequency, measured Sagittarius A* as half that size.

A mass equal to four million Suns is known to lie within Sagittarius A*, and the new measurement makes the case for a black hole even more compelling than it was previously. Scientists simply don't know of any long-lasting object other than a black hole that could contain this much mass in such a small area. However, they would like to see even stronger proof of a black hole.

"The extremely strong gravitational pull of a black hole has several effects that would produce a distinctive 'shadow' that we think we could see if we can image details about half as small as those in our latest images," said Fred K.Y. Lo, Director of the National Radio Astronomy Observatory and another member of the research team. "Seeing that shadow would be the final proof that a supermassive black hole is at the center of our Galaxy," Lo added.

Many galaxies are believed to have supermassive black holes at their centers, and many of these are much more massive than the Milky Way's black hole. Also, in many other galaxies, the gravitational energy of the black hole is powering superfast "jets" of subatomic particles at nearly the speed of light. Such jets in other galaxies extend outward for thousands of light-years.

The Milky Way's central black hole is much less active than that of many other galaxies, presumably because it has less nearby material to "eat." Astronomers believe that the radio waves they see coming from Sagittarius A* probably are generated by particle jets much shorter than those of more-active galaxies.

By observing the object at higher radio frequencies, scientists have detected parts of the jets ever closer to the black hole. The results announced last year were based on observations at 43 Ghz, and the latest observations were made at 86 Ghz.

"We believe that if we can double the frequency again, we will see the black-hole shadow produced by effects of Einstein's General Relativity theory," Lo said.

In a few years, when the Atacama Large Millimeter Array (ALMA) comes on line, it may be used in conjunction with other millimeter-wave telescopes to make the higher-frequency observations that will reveal the telltale black-hole shadow.

At a distance of 26,000 light-years, the Milky Way's central black hole is the closest such supermassive object. That makes it the most likely one to finally reveal the concrete evidence for a black hole that astronomers have sought for years.

Shen and Lo worked with Mao-Chang Liang of Caltech, Paul Ho of the Harvard-Smithsonian Center for Astrophysics (CfA) and the Institute of Astronomy & Astrophysics of the Academia Sinica in Taiwan, and Jun-Hui Zhao of CfA. The astronomers published their findings in the November 3 issue of the scientific journal Nature.

Source: National Radio Astronomy Observatory

Explore further: NASA's reliance on outsourcing launches causes a dilemma for the space agency

Related Stories

VLA reveals 'bashful' black hole in neighboring galaxy

Jun 17, 2015

Thanks to the extraordinary sensitivity of the Karl G. Jansky Very Large Array (VLA), astronomers have detected what they believe is the long-sought radio emission coming from a supermassive black hole at ...

Monster black hole wakes up after 26 years

Jun 25, 2015

Over the past week, ESA's Integral satellite has been observing an exceptional outburst of high-energy light produced by a black hole that is devouring material from its stellar companion.

How the brightest lights in the universe 'flicker'

Jun 24, 2015

Active galactic nuclei are the brightest objects in the universe. They are not lit up permanently, but rather 'flicker' extremely slowly. This insight helps ETH researchers better understand the influence ...

Recommended for you

Hubble view: Wolf-Rayet stars, intense and short-lived

Jul 03, 2015

This NASA/European Space Agency (ESA) Hubble Space Telescope picture shows a galaxy named SBS 1415+437 (also called SDSS CGB 12067.1), located about 45 million light-years from Earth. SBS 1415+437 is a Wolf-Rayet ...

Crash test assesses plane emergency locator transmitters

Jul 03, 2015

The Cessna 172 airplane dangled 82 feet in the air – looking almost like it was coming in for a landing, except for the cables attaching it to a huge gantry at NASA's Langley Research Center in Hampton, ...

NASA image: Curiosity's stars and stripes

Jul 03, 2015

This view of the American flag medallion on NASA's Mars rover Curiosity was taken by the rover's Mars Hand Lens Imager (MAHLI) during the 44th Martian day, or sol, of Curiosity's work on Mars (Sept. 19, 2012). ...

NASA image: Stellar sparklers that last

Jul 03, 2015

While fireworks only last a short time here on Earth, a bundle of cosmic sparklers in a nearby cluster of stars will be going off for a very long time. NGC 1333 is a star cluster populated with many young ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.