# Time according to the gravity of Sagittarius A*?

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This may be a really dumb question (I'm more of a Biologist than an Astronomer) so I apologize in advance for my little knowledge pertaining to Astronomy, but, if I'm not mistaken, time is effected by gravity, right? So what is Sagittarius A*'s time compared to ours since it has so much stronger gravity? Do we know specifically the difference?

Not at all a dumb question. As you have heard, it is true that time is affected by gravity. The stronger the gravitational field, the slower time passes. If you're far from any gravitating matter, time passes "normally".

But to answer your question, we must specify what is meant by "the black holes's time" (let's call the black hole $$mathrm{BH}_mathrm{Sgr,A^*}$$; see note below on the nomenclature), since it depends on how far from Sgr A* we are talking. The time pace at a distance $$r$$ from the center of a BH is given by $$t = t_infty sqrt{1 - frac{r_mathrm{S}}{r}},$$ where $$t_infty$$ is the time "at infinity", i.e. far from the BH, and $$r_mathrm{S} equiv frac{2GM}{c^2} simeq 3,mathrm{km}, imes left( frac{M}{M_odot} ight)$$ is the so-called Schwarzschild radius (the "surface" of the BH), which is where not even light can escape. Here, $$G$$ is the gravitational constant, $$M$$ is the mass of the BH, $$c$$ is the speed of light, and $$M_odot$$ is the mass of the Sun.

The last equality shows that a BH with the mass of the Sun would have a radius of 3 km. The mass of $$mathrm{BH}_mathrm{Sgr,A^*}$$ is some 4.1 million Solar masses, so its radius is $$r_mathrm{S} = 12.1$$ million km.

Plugging in the other numbers, we can see that at a distance from $$mathrm{BH}_mathrm{Sgr,A^*}$$ of

1. 1 lightyear, time runs slower by a factor of 1.00000064, i.e. unnoticeably.
2. 1 astronomical unit (the distance from Earth to the Sun), time runs 4% slower.
3. 1 million km from the surface, time runs slower by a factor of 3.6.
4. 1000 km from the surface, time runs slower by a factor of 110.
5. 1 km from the surface, time runs slower by a factor of ~3500.
6. 1 m from the surface, time runs more than a 100,000 times slower.
7. At the surface, time stops.

Note that this time dilation is what a distant observer (i.e. the guy with the $$t_infty$$ time) would measure for an observer at the distance $$r$$. The person at $$r$$ would just measure his/her own time as usual. For instance, according to point 5 above, if you were hovering 1 km from the surface, waving your hand every second, then I, choosing to stay at a safe distance of 1 lightyear but with a magically powerful telescope, would see you wave approximately once every hour. And when you run out of fuel and plummet into the BH, then when you cross the surface you wouldn't notice anything particular, but I would see you frozen in time. This is the concept of relativity.

Finally, let me use this chance to clarify something that people, including myself, often have gotten wrong: Sagittarius A (without an asterisk) is a radio source in the center of the Milky Way. It consists of three parts: Sagittarius A East (a supernova remnant), Sagittarius A West (dust and gas clouds), and Sagittarius A*, or Sgr A*, which is a very bright and compact radio source believed to be formed by a supermassive BH. Sgr A* isn't actually the BH itself. I think the BH doesn't really have a name, so I'll call it $$mathrm{BH}_mathrm{Sgr,A^*}$$. Maybe that's a bad name…

## Did the Milky Way's huge black hole kill all the red giants around it?

Powerful jets launched from Sagittarius A* may have stripped the stars' atmospheres away.

Beginning in the 1990s, astronomers noticed a disturbing lack of red giant stars in the Milky Way's center.

Theories abounded to explain the absence, and now a new theory proposes something truly frightening: a massive jet launched from our galaxy's supermassive black hole destroyed any red giants that wandered into its path.

## Astronomers Spot Unprecedented Flashes From Our Galaxy's Black Hole

An attempt to prove Einstein’s hallmark theory of gravity revealed something even freakier: an unprecedented flash from the black hole at the center of our galaxy.

The Milky Way features a black hole that’s 4 million times the mass of the Sun, called Sagittarius A* (pronounced A-star). Te ams of scientists have been measuring it for over 20 years, and back in May, one team observed a flash of infrared radiation that was brighter than had ever been measured from the black hole. It’s not something to worry about, but it will be an exciting development for astronomers to try and understand.

“We can see it changing in real time,” Tuan Do, the study’s first author and an associated research scientist at UCLA, told Gizmodo. “You usually don’t get to do that in astrophysics.”

The team of scientists observed the galactic center for four nights this year using an infrared camera on the Keck II Telescope. On May 13, the amount of infrared light it emitted increased by 75 times in just two hours, according to the paper published in Astrophysical Journal Letters. It also flashed brightly on April 20, and dimmed quickly on the nights it flashed. Do explained that the statistical analysis that followed the observation demonstrated that the event was unu sual.

Black holes are objects so dense that beyond a zone called the event horizon, their gravitational field warps space to the point that light can’t escape. But they can still spew radiation from outside their event horizon, the result of interaction with gas and stars that come too close .

## Einstein's General Relativity: Star Orbiting a Supermassive Black Hole Proves Famous Theory Right (Again)

An international team of scientists have completed the first successful test of Albert Einstein's famous theory of general relativity (GR) near a supermassive black hole, according to a study published in the journal Astronomy & Astrophysics.

Using the European Southern Observatory's (ESO) Very Large Telescope (VLT) in the Atacama Desert, Chile, researchers demonstrated that the theory accurately predicted the motion of a star passing through the extreme gravitational field surrounding Sagittarius A*&mdashthe supermassive black hole that is thought to reside 26,000 light-years from Earth at the center of the Milky Way.

This black hole has a mass equivalent to four million Suns and is encircled by a small group of stars orbiting it at high incredibly high speeds. The characteristics of this extreme environment make it an ideal place for scientists to test general relativity.

GR, which revolutionized science after its publication in 1915, describes the nature of gravity. It says that spacetime&mdasha fusion of the three dimensions of space and the single dimension of time&mdashis deformed by massive objects, such as black holes, and that this deformation affects the movement of objects in the Universe.

"There have been lots of tests of different predictions of GR&mdashin tabletop experiments, in the Solar System, and in binary pulsar systems," Ingrid Stairs, an astrophysicist from the University of British Columbia, who was not involved in the study, previously told Newsweek.

But despite this, GR has never failed. In other words, general relativity accurately describes the nature of gravity in all the situations it has been tested in.

"That might sound remarkable&mdashbut if it ever failed, people would've given up on that theory," Stefan Gillessen, an author of the latest study from the Max-Planck Institute for Extraterrestrial Physics, told Newsweek.

Nevertheless, scientists are continually assessing the theory to make sure that these laws apply in all situations. These experiments could shed light on some of the biggest questions in physics, such as how to reconcile general relativity&mdashwhich is good at describing massive objects&mdashand quantum mechanics&mdashthe bizarre physics of the very small.

For the latest test of GR, scientists used precise infrared-detecting instruments on the VLT to track one of the fast-orbiting stars around Sagittarius A*, known as S2, as it passed "close" to the black hole in May 2018. At this point in time, S2 came within about 12 billion miles of the black hole while moving at speeds of more than 15 million miles per hour.

The team compared position and velocity measurements of the star made by the VLT's various instruments, as well as previous observations of S2, with the predictions made by general relativity, Isaac Newton's simpler theory of gravity, and alternative theories of gravity.

The results&mdashwhich are the culmination of 26 years of ever-more-precise observations of our galaxy's center with ESO instruments&mdashagreed precisely with the predictions found in general relativity, according to the researchers. However, they were inconsistent with Newton's theory&mdashthe first time that a deviation from his predictions have been observed in the motion of a star around a black hole.

The findings revealed a clear effect called gravitational redshift where light from S2 was stretched to longer wavelengths by the extreme gravitational field of the supermassive black hole&mdasha process that agrees precisely with GR.

"This is the second time that we have observed the close passage of S2 around the black hole in our galactic center," Reinhard Genzel, Director of the Max Planck Institute for Extraterrestrial Physics and an author of the study, said in a statement.

"But this time, because of much improved instrumentation, we were able to observe the star with unprecedented resolution," he said. "We have been preparing intensely for this event over several years, as we wanted to make the most of this unique opportunity to observe general relativistic effects."

The findings are significant because they prove that Einstein's theory works even in extreme environments, according to Françoise Delplancke, head of the System Engineering Department at ESO.

"Here in the Solar System we can only test the laws of physics now and under certain circumstances," he said in the statement. "So, it's very important in astronomy to also check that those laws are still valid where the gravitational fields are very much stronger."

The new study is just the latest in a series of publications proving Einstein right.

In a paper published earlier this month, scientists demonstrated that Einstein's general theory of relativity (GR) works in other extreme gravitational environments. Meanwhile, a different paper published in June confirmed that GR can accurately describe the behavior of gravity in distant galaxies.

Finally, new findings from researchers at the Department of Energy's Oak Ridge National Laboratory have supported a theory first proposed by Albert Einstein in 1911 that explains how heat moves through solids.

The Very Large Telescope is ESO's flagship facility and the world's most advanced visible-light astronomical observatory, consisting of four Unit Telescopes with main mirrors measuring 8.2 meters in diameter.

The telescopes can work together by combining light beams they detect using a complex system of subterranean mirrors in order to reconstruct images with a resolution equivalent to distinguishing the two headlights of a car at the distance of the Moon.

## Some Weird Gas Balls Are Swirling Around Sagittarius A*

Something weird is happening in the center of our universe.

Researchers have discovered a slew of what they believe to be a brand-spanking-new class of objects&mdashcalled G objects&mdashcircling the Sagittarius A*, the supermassive black hole at the center of the galaxy.

They behave strangely, too&mdashlike stars, instead of the clouds of gas to which their spectral signatures point. And when they sweep close to the black hole, their normally compact form begins to warp and stretch. The first sighting of these twisty masses of gas and dust occurred nearly 20 years ago, and researchers have been trying to unravel their secrets since.

Four more of these curious celestial objects have been identified, according to research published this week in the journal Nature. They follow vastly different orbits than the first two objects, G1 and G2, which have orbital periods stretching from 170 years to 1,600 years. The researchers analyzed 13 years worth of data gathered from Keck Observatory on Mauna Kea to better understand how these objects form.

Astronomers may finally have some clues. They observed that when G2 got close to Sagittarius A*, it began to stretch out. &ldquoIt went from being a pretty innocuous object when it was far from the black hole to one that was really stretched out and distorted at its closest approach and lost its outer shell, and now it's getting more compact again," astrophysicist Andrea Ghez of the University of California, Los Angeles said in a statement.

This means something kept the hazy gas ball intact, despite the enormous force exerted on it by the black hole. Ghez and her team suspect the objects may form from binary star systems, where two stars orbit each other, that collapse into themselves. A massive star may be hiding inside the ball of gas, as a result of the collapse.

Of course, Ghez and her team will continue to search for objects in this exciting new class. The recent batch of evidence suggests they could be more common that astronomers previously believed.

## X-Ray Observations of Milky Way’s Supermassive Black Hole Reveal Unusual Activity

A long monitoring campaign of the Milky Way’s black hole, called Sagittarius A*, has revealed some unusual activity. Typically relatively quiet, the 4-million-solar-mass black hole had an increase in X-ray flares in 2014. The timing of this surge coincided with the passage close to Sagittarius A* of a mysterious object called G2.

The upper two panels of this graphic represent a possible explanation for a recent increase in X-ray flares from Sagittarius A* seen by three X-ray telescopes. As part of a long monitoring campaign, astronomers observed the black hole as a mysterious object called G2 appeared to pass close to the black hole. The timing of G2’s passage could suggest that material from G2 caused the surge in X-ray activity, but it is also possible that this unrelated behavior of Sagittarius A*. The bottom panel is a view of the region around the black hole where red, green, and blue represent low, medium, and high-energy X-rays detected by NASA’s Chandra X-ray Observatory. Sagittarius A* itself is not visible in this image, but is embedded in the white dot at the end of the arrow. Image credit: NASA / CXC / MPE / G.Ponti et al. / M.Weiss.

By combining information from monitoring campaign by three X-ray space telescopes – ESA’s XMM-Newton, NASA’s Chandra X-ray Observatory and NASA’s Swift satellite, a team of astronomers was able to trace the activity of Sagittarius A* over the last 15 years (from September 1999 through November 2014).

Sagittarius A* has been producing one bright X-ray flare about every 10 days, according to the team, led by Dr Gabriele Ponti of the Max Planck Institute for Extraterrestrial Physics.

However, within the past year, there has been a 10-fold increase in the rate of flares from the black hole, at about one every day. This increase happened soon after the close approach to the black hole by G2.

Astronomers have been tracking G2 for years, originally thinking it was an extended cloud of gas and dust.

However, after passing close to Sagittarius A* in late 2013 its appearance did not change much, apart from being slightly stretched by the gravity of the black hole.

This led to new theories that G2 was not a gas cloud, but instead a star or pair of stars within an extended dusty cocoon.

“For several years, we’ve been tracking the X-ray emission from Sagittarius A*. This includes also the close passage of this dusty object. A year or so ago, we thought it had absolutely no effect on Sagittarius A*, but our new data raise the possibility that that might not be the case,” said Dr Ponti, who is the lead author of a paper accepted for publication by the Monthly Notices of the Royal Astronomical Society (arXiv.org preprint).

If the G2 explanation does explain the recent rise in X-ray flares, it would be the first sign of excess material falling onto the black hole because of the cloud’s close passage.

Some gas would likely have been stripped off the cloud, and captured by the gravity of Sagittarius A*. It then could have started interacting with hot material flowing towards the black hole, resulting in an enhanced feeding rate and the production of X-ray flares.

While the timing of G2’s passage with the surge in X-rays from the black hole is intriguing, it is not yet an open-and-shut case.

That is because scientists see other black holes that appear to have behavior similar to the most recent increase of activity from the Milky Way’s black hole.

Therefore, it’s possible this increased chatter from Sagittarius A* may be a common trait among supermassive black holes and unrelated to G2.

Instead, it could represent, for example, a change in the strength of winds from nearby massive stars that are feeding the black hole.

“It’s too soon to say for sure, but we will be keeping X-ray eyes on Sagittarius A* in the coming months. Hopefully, new observations will tell us whether G2 is responsible for the changed behavior or if the new flaring is just part of how the black hole behaves,” said study co-author Dr Barbara De Marco of the Max Planck Institute for Extraterrestrial Physics.

G. Ponti et al. 2015. Fifteen years of XMM-Newton and Chandra monitoring of Sgr A*: Evidence for a recent increase in the bright flaring rate. Mon. Not. R. Astron. Soc., accepted for publication arXiv: 1507.02690

## Radio Astronomers Lift "Fog" on Milky Way's Dark Heart: Black Hole Fits Inside Earth's Orbit

Thirty years after astronomers discovered the mysterious object at the exact center of our Milky Way Galaxy, an international team of scientists has finally succeeded in directly measuring the size of that object, which surrounds a black hole nearly four million times more massive than the Sun. This is the closest telescopic approach to a black hole so far and puts a major frontier of astrophysics within reach of future observations. The scientists used the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope to make the breakthrough.

"This is a big step forward," said Geoffrey Bower, of the University of California-Berkeley. "This is something that people have wanted to do for 30 years," since the Galactic center object, called Sagittarius A* (pronounced "A-star"), was discovered in 1974. The astronomers reported their research in the April 1 edition of Science Express.

"Now we have a size for the object, but the mystery about its exact nature still remains," Bower added. The next step, he explained, is to learn its shape, "so we can tell if it is jets, a thin disk, or a spherical cloud."

The Milky Way's center, 26,000 light-years from Earth, is obscured by dust, so visible-light telescopes cannot study the object. While radio waves from the Galaxy's central region can penetrate the dust, they are scattered by turbulent charged plasma in the space along the line of sight to Earth. This scattering had frustrated earlier attempts to measure the size of the central object, just as fog blurs the glare of distant lighthouses.

"After 30 years, radio telescopes finally have lifted the fog and we can see what is going on," said Heino Falcke, of the Westerbork Radio Observatory in the Netherlands, another member of the research team.

The bright, radio-emitting object would fit neatly just inside the path of the Earth's orbit around the Sun, the astronomers said. The black hole itself, they calculate, is about 14 million miles across, and would fit easily inside the orbit of Mercury. Black holes are concentrations of matter so dense that not even light can escape their powerful gravity.

The new VLBA observations provided astronomers their best look yet at a black hole system. "We are much closer to seeing the effects of a black hole on its environment here than anywhere else," Bower said.

The Milky Way's central black hole, like its more-massive cousins in more-active galactic nuclei, is believed to be drawing in material from its surroundings, and in the process powering the emission of the radio waves. While the new VLBA observations have not provided a final answer on the nature of this process, they have helped rule out some theories, Bower said. Based on the latest work, he explained, the top remaining theories for the nature of the radio- emitting object are jets of subatomic particles, similar to those seen in radio galaxies and some theories involving matter being accelerated near the edge of the black hole.

As the astronomers studied Sagittarius A* at higher and higher radio frequencies, the apparent size of the object became smaller. This fact, too, Bower said, helped rule out some ideas of the object's nature. The decrease in observed size with increasing frequency, or shorter wavelength, also gives the astronomers a tantalizing target.

"We think we can eventually observe at short enough wavelengths that we will see a cutoff when we reach the size of the black hole itself," Bower said. In addition, he said, "in future observations, we hope to see a 'shadow' cast by a gravitational lensing effect of the very strong gravity of the black hole."

In 2000, Falcke and his colleagues proposed such an observation on theoretical grounds, and it now seems feasible. "Imaging the shadow of the black hole's event horizon is now within our reach, if we work hard enough in the coming years," Falcke added.

Another conclusion the scientists reached is that "the total mass of the black hole is very concentrated," according to Bower. The new VLBA observations provide, he said, the "most precise localization of the mass of a supermassive black hole ever." The precision of these observations allows the scientists to say that a mass of at least 40,000 Suns has to reside in a space corresponding to the size of the Earth's orbit. However, that figure represents only a lower limit on the mass. Most likely, the scientists believe, all the black hole's mass -- equal to four million Suns -- is concentrated well inside the area engulfed by the radio-emitting object.

To make their measurement, the astronomers had to go to painstaking lengths to circumvent the scattering effect of the plasma "fog" between Sagittarius A* and Earth. "We had to push our technique really hard," Bower said.

Bower likened the task to "trying to see your yellow rubber duckie through the frosted glass of the shower stall." By making many observations, only keeping the highest-quality data, and mathematically removing the scattering effect of the plasma, the scientists succeeded in making the first-ever measurement of Sagittarius A*'s size.

In addition to Bower and Falcke, the research team includes Robin Herrnstein of Columbia University, Jun-Hui Zhao of the Harvard-Smithsonian Center for Astrophysics, Miller Goss of the National Radio Astronomy Observatory, and Donald Backer of the University of California-Berkeley. Falcke also is an adjunct professor at the University of Nijmegen and a visiting scientist at the Max-Planck Institute for Radioastronomy in Bonn, Germany.

Sagittarius A* was discovered in February of 1974 by Bruce Balick, now at the University of Washington, and Robert Brown, now director of the National Astronomy and Ionospheric Center at Cornell University. It has been shown conclusively to be the center of the Milky Way, around which the rest of the Galaxy rotates. In 1999, Mark Reid of the Harvard-Smithsonian Center for Astrophysics and his colleagues used VLBA observations of Sagittarius A* to detect the Earth's motion in orbit around the Galaxy's center and determined that our Solar System takes 226 million years to make one circuit around the Galaxy.

In March 2004, 55 astronomers gathered at the National Radio Astronomy Observatory facility in Green Bank, West Virginia, for a scientific conference celebrating the discovery of Sagittarius A* at Green Bank 30 years ago. At this conference, the scientists unveiled a commemorative plaque on one of the discovery telescopes.

The Very Long Baseline Array, part of the National Radio Astronomy Observatory, is a continent-wide radio-telescope system, with 10, 240-ton dish antennas ranging from Hawaii to the Caribbean. It provides the greatest resolving power, or ability to see fine detail, of any telescope in astronomy, on Earth or in space.

The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

## Milky Way snack time: Supermassive black hole to consume gas cloud

As Sagittarius A* is located almost 26,000 light years away from the Earth, the collision itself took place… well, 26,000 years ago. Now, for the first time in history, astronomers will be able to monitor the feeding of a black hole

According to scientific models of the Max Planck Institute for Extraterrestrial Physics in Germany, G2’s elliptical orbit will pass the event horizon, the point-of-no-return from the black hole’s grasp, around March 31. The closest distance from the black hole’s core will be about 130 AU (astronomical unit, roughly Earth’s distance from the Sun).

"Everyone wants to see the event happening because it's so rare,"said Nathalie Degenaar, who is a Hubble researcher in the Department of Astronomy at the College of Literature, Science, and the Arts at the University of Michigan.

The gaseous object, G2, discovered in 2011 by the European Science Organization, is about three times the mass of Earth. Travelling on a highly eccentric orbit, it is quickly approaching the galaxy's central black hole, and as it comes nearer it heats up and its speed increases, turning it into something akin to a giant piece of string.

However, scientists are in doubt whether it is all gas or contains an old star.

In case it is a gas cloud, the invisible space monster will slowly swallow it up for years, creating an impressive show available in the X-ray band. But, if G2 actually hides an old star, its gravitational force would prevent the whole cloud from slipping into the black hole.

"I would be delighted if Sagittarius A* suddenly became 10,000 times brighter. However, it is possible that it will not react muchlike a horse that won't drink when led to water," said Jon Miller, a University of Michigan associate professor of astronomy who also works on the project. "If Sagittarius A* consumes some of G2, we can learn about black holes accreting at low levelssneaking midnight snacks. It is potentially a unique window into how most black holes in the present-day universe accrete."

The Milky Way's 4 million-solar mass supermassive black hole, Sagittarius A* can be found in the southern summer sky near the constellations of Sagittarius and Scorpius. It is actually quite dim, and the highly anticipated ‘meal’, already transformed into ‘spaghetti’ by the black hole’s enormous gravity, may lighten it up a bit.

"We think that the fainter ones are the majority, but it's very difficult to study those," Degenaar said on supermassive black holes that are believed to compose the centers of all elliptical and spiral galaxies. "We just can't see them. Ours is the only one we can study to understand what their role is in the universe."

The strangeness, in addition to enigmatic properties of space and time in proximity to black holes, has secured them considerable interest not only of scientists, but also of science fiction writers. The history of black holes dates back to the 18th century, when they were first imagined as “black stars” that absorb light. But later on, black holes came to be defined as “compact” objects (that is, having enough mass in a small enough volume) with gravity so extreme that nothing can escape it – even light, regarded as the fastest thing in the universe.

"They eat matter from their surroundings and blow matter back. The way they do that influences the evolution of the entire galaxyhow stars are formed, how the galaxy grows, how it interacts with other galaxies," Degenaar said. "Even more broadly, the way galaxies evolved is important for the evolution of the whole universe, how it came into being and how it's changing."

## 'Mind-boggling' monster black hole at Milky Way's center seen by scientists

Astronomers have spotted a supermassive black hole called Sagittatius A* at the center of the Milky Way galaxy. They say it’s pulling gas blobs into its vortex at 30 percent the speed of light.

Astronomers have observed a stunning, supermassive black hole at the center of the Milky Way that's pulling gas blobs into its vortex at 30 percent of the speed of light.

This is the first time that material has been observed orbiting close to the point of no return, and the most detailed observations yet of material orbiting so close to a black hole, according to scientists at the European Southern Observatory

The movement of the gas blobs triggered powerful bursts of radiation that were then detected by researchers using the GRAVITY instrument on the Very Large Telescope array in Chile.

This simulation shows a hot blob of gas falling toward a black hole at 30 percent of the speed of light. (ESO/Gravity Consortium/L. Calçada)

"It’s mind-boggling to actually witness material orbiting a massive black hole at 30 percent of the speed of light," said Oliver Pfuhl, a scientist at the Max Planck Institute for Extraterrestrial Physics (MPE), in a statement. "GRAVITY’s tremendous sensitivity has allowed us to observe the accretion processes in real time in unprecedented detail."

According to researchers, the monster black hole, known as Sagittarius A* (pronounced "A-star"), is a physical point of no return that pulls any matter that's too close into a death spiral.

The group published a study of its work in the Journal of Astronomy & Astrophysics on Wednesday.

Sagittarius A* is thought to be a black hole with a mass that's more than 4 million times the mass of our sun, residing about 25,000 light-years from Earth.

"This always was one of our dream projects but we did not dare to hope that it would become possible so soon," said Reinhard Genzel, also of the MPE, who led the study.

Referring to the long-standing assumption that Sagittarius A* is a supermassive black hole, Genzel concluded that "the result is a resounding confirmation of the massive black hole paradigm."

The European Southern Observatory also created an animation of the gas cloud and flares, seen below.

The incident observed by astronomers is depicted in the image at the top of this story, however, the image is not a photograph. It's a visual simulation based on data collected by GRAVITY and other telescopes.

"If you were close enough to observe these flares, you'd be in a lot of trouble," Tana Joseph, an astrophysicist and fellow at the University of Manchester who wasn't involved in the study, told Business Insider. "We would see extremely bright flashes of optical light, and there would be lots of high energy radiation, like gamma rays and X-rays, that would be very damaging to our bodies."

## Time according to the gravity of Sagittarius A*? - Astronomy

Thirty years after astronomers discovered the mysterious object at the exact center of our Milky Way Galaxy, an international team of scientists has finally succeeded in directly measuring the size of that object, which surrounds a black hole nearly four million times more massive than the Sun. This is the closest telescopic approach to a black hole so far and puts a major frontier of astrophysics within reach of future observations. The scientists used the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope to make the breakthrough. Milky Way Nucleus 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 (Click on Image for Larger Version)

"This is a big step forward," said Geoffrey Bower, of the University of California-Berkeley. "This is something that people have wanted to do for 30 years," since the Galactic center object, called Sagittarius A* (pronounced "A-star"), was discovered in 1974. The astronomers reported their research in the April 1 edition of Science Express.

"Now we have a size for the object, but the mystery about its exact nature still remains," Bower added. The next step, he explained, is to learn its shape, "so we can tell if it is jets, a thin disk, or a spherical cloud."

The Milky Way's center, 26,000 light-years from Earth, is obscured by dust, so visible-light telescopes cannot study the object. While radio waves from the Galaxy's central region can penetrate the dust, they are scattered by turbulent charged plasma in the space along the line of sight to Earth. This scattering had frustrated earlier attempts to measure the size of the central object, just as fog blurs the glare of distant lighthouses.

"After 30 years, radio telescopes finally have lifted the fog and we can see what is going on," said Heino Falcke, of the Westerbork Radio Observatory in the Netherlands, another member of the research team.

The bright, radio-emitting object would fit neatly just inside the path of the Earth's orbit around the Sun, the astronomers said. The black hole itself, they calculate, is about 14 million miles across, and would fit easily inside the orbit of Mercury. Black holes are concentrations of matter so dense that not even light can escape their powerful gravity.

The new VLBA observations provided astronomers their best look yet at a black hole system. "We are much closer to seeing the effects of a black hole on its environment here than anywhere else," Bower said.

The Milky Way's central black hole, like its more-massive cousins in more-active galactic nuclei, is believed to be drawing in material from its surroundings, and in the process powering the emission of the radio waves. While the new VLBA observations have not provided a final answer on the nature of this process, they have helped rule out some theories, Bower said. Based on the latest work, he explained, the top remaining theories for the nature of the radio- emitting object are jets of subatomic particles, similar to those seen in radio galaxies and some theories involving matter being accelerated near the edge of the black hole.

As the astronomers studied Sagittarius A* at higher and higher radio frequencies, the apparent size of the object became smaller. This fact, too, Bower said, helped rule out some ideas of the object's nature. The decrease in observed size with increasing frequency, or shorter wavelength, also gives the astronomers a tantalizing target.

"We think we can eventually observe at short enough wavelengths that we will see a cutoff when we reach the size of the black hole itself," Bower said. In addition, he said, "in future observations, we hope to see a 'shadow' cast by a gravitational lensing effect of the very strong gravity of the black hole."

In 2000, Falcke and his colleagues proposed such an observation on theoretical grounds, and it now seems feasible. "Imaging the shadow of the black hole's event horizon is now within our reach, if we work hard enough in the coming years," Falcke added.

Another conclusion the scientists reached is that "the total mass of the black hole is very concentrated," according to Bower. The new VLBA observations provide, he said, the "most precise localization of the mass of a supermassive black hole ever." The precision of these observations allows the scientists to say that a mass of at least 40,000 Suns has to reside in a space corresponding to the size of the Earth's orbit. However, that figure represents only a lower limit on the mass. Most likely, the scientists believe, all the black hole's mass -- equal to four million Suns -- is concentrated well inside the area engulfed by the radio-emitting object.

To make their measurement, the astronomers had to go to painstaking lengths to circumvent the scattering effect of the plasma "fog" between Sagittarius A* and Earth. "We had to push our technique really hard," Bower said.

Bower likened the task to "trying to see your yellow rubber duckie through the frosted glass of the shower stall." By making many observations, only keeping the highest-quality data, and mathematically removing the scattering effect of the plasma, the scientists succeeded in making the first-ever measurement of Sagittarius A*'s size. The VLBA The VLBA

In addition to Bower and Falcke, the research team includes Robin Herrnstein of Columbia University, Jun-Hui Zhao of the Harvard-Smithsonian Center for Astrophysics, Miller Goss of the National Radio Astronomy Observatory, and Donald Backer of the University of California-Berkeley. Falcke also is an adjunct professor at the University of Nijmegen and a visiting scientist at the Max-Planck Institute for Radioastronomy in Bonn, Germany.

Sagittarius A* was discovered in February of 1974 by Bruce Balick, now at the University of Washington, and Robert Brown, now director of the National Astronomy and Ionospheric Center at Cornell University. It has been shown conclusively to be the center of the Milky Way, around which the rest of the Galaxy rotates. In 1999, Mark Reid of the Harvard-Smithsonian Center for Astrophysics and his colleagues used VLBA observations of Sagittarius A* to detect the Earth's motion in orbit around the Galaxy's center and determined that our Solar System takes 226 million years to make one circuit around the Galaxy.

In March 2004, 55 astronomers gathered at the National Radio Astronomy Observatory facility in Green Bank, West Virginia, for a scientific conference celebrating the discovery of Sagittarius A* at Green Bank 30 years ago. At this conference, the scientists unveiled a commemorative plaque on one of the discovery telescopes.

The Very Long Baseline Array, part of the National Radio Astronomy Observatory, is a continent-wide radio-telescope system, with 10, 240-ton dish antennas ranging from Hawaii to the Caribbean. It provides the greatest resolving power, or ability to see fine detail, of any telescope in astronomy, on Earth or in space.

The National Radio Astronomy Observatory is a facility of the National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.