Astronomy

How the position of this black hole known?

How the position of this black hole known?


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How do scientists know the positions of black holes?
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The article is referring to the black hole known as V4641 Sagittarii. It was originally thought to be the closest known black hole to Earth, at 1,600 light-years (0.5 kiloparsecs). It's a binary system which emits X-rays. Original distance measurements were made based on observations during and following an X-ray outburst in 1999. Analysis of the jets emitted and of the inclination of the system led to initial estimates of $0.4$-$1.7 ext{ kpc}$ (see Hjellming et al. (2000)), with lower estimates of around $sim0.5 ext{ kpc}$ being favored - the distance that was then commonly quoted.

Later spectroscopic measurements in more detail appear to show these early observations to be incorrect, as Orosz et al. (2000) found. By observing the orbits of the two objects in the system, their masses were determined, which led to an estimate of the companion star's radius. The temperature of the star was determined by examining its spectrum, and its luminosity was computed from this and the radius. By using the color index and taking into account interstellar extinction, the group was able to calculate the distance to the companion star, and thus to the black hole. They found $7.40leq dleq12.31 ext{ kpc}$, values closer to the currently accepted distance.

An absorption study (Chaty et al. (2001)) found values somewhere in the middle, with $3leq dleq8 ext{ kpc}$. However, all groups agree that the actual distance to V4641 Sagittarii is much further than 1,600 light-years. The closest known black hole is now thought to be A0620-00, also known as V616 Monocerotis, at around 2,800 light-years (about $0.85 ext{ kpc}$) from Earth.


General black hole detection is discussed in the answers to How are black holes found?. The takeaway for this case - a stellar-mass black hole in a binary system - is that effects from the companion star must be observed and measured. Fortunately, there are typically plenty of ways to choose from.


How the position of this black hole known? - Astronomy

I am a student in physics at Bishop Luers High School, Fort Wayne, Indiana. We have been studying physics and this is part of an assignment from my teacher. Here is my question: How far away is the closest black hole?

The closest known black holes are stellar mass black holes in our galaxy. These black holes have so far only been seen when they are in close contact with another star which is orbiting around them (well really they orbit each other). The black hole accretes material from the star and this produces a lot of energy. When jets are produced the systems are known as microquasars (by analogy with extragalactic quasars) and can be observed at many wavelengths, but usually are most distinctive in X-rays.

Here is a page with a summary of known microquasars. Note: not all black hole systems that are known are microquasars.

All of these microquasars are within about 24 thousand light years of Earth. As of now the closest known one is thought to lie at about 1,600 light years from Earth. You can read about it in this space.com article.

Update by Michael Lam, July 17, 2015: This question was answered in February, 2002. However, observations published in July, 2001 showed that V4641 Sgr, mentioned in the space.com article, had to be at least 15 times farther away than previously thought. The current nearest, published in 2007, is V616 Mon, also known as A0620-00. Additional information can be found via the University of Texas McDonald Observatory StarDate page (last modified 2/12/2012).

This page was last updated July 17, 2015.

About the Author

Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.


Astronomers Find ‘Nearly Naked’ Supermassive Black Hole Two Billion Light-Years Away

A team of scientists led by National Radio Astronomy Observatory astronomer James Condon has found the shredded remains of a small galaxy that passed through a larger one, leaving only the smaller galaxy’s black hole to emerge and speed away at more than 2,000 miles per second.

Left: this deep Hubble image of the galaxy cluster ZwCl 1715.5+4229 (also known as ZwCl 8193) shows the full extent of the giant galaxy 2MASX 17171926+4226571 and some of its gravitationally lensed background galaxies. The white ‘X’ marks the VLBA radio position, the white ‘+’ marks the Hubble optical position of the giant galaxy’s core, and the white box bounds the zoomed image at right. Right: this shallower zoomed Hubble image of the galaxy cluster reveals the core of the giant galaxy, the smaller galaxy, several cluster galaxies, and extended interaction debris. The Hubble position of the giant galaxy’s core is marked by the white ‘+,’ and optical identification of B3 1715+425 is enclosed by a white circle centered on its Hubble position. Image credit: J.J. Condon et al / NASA / ESA / Hubble / NSF / VLBA.

“We were looking for orbiting pairs of supermassive black holes, with one offset from the center of a galaxy, as telltale evidence of a previous galaxy merger,” Dr. Condon said.

“Instead, we found this black hole fleeing from the larger galaxy and leaving a trail of debris behind it. We’ve not seen anything like this before.”

Dr. Condon and his colleagues from the University of Colorado, Max-Planck-Institute for Radio Astronomy and Astrogeo Center began their quest by using NSF’s Very Long Baseline Array (VLBA) to make images of more than 1,200 galaxies.

The VLBA observations showed that the supermassive black holes of nearly all these galaxies were at the centers of the galaxies.

However, one object, in ZwCl 1715.5+4229, a massive cluster of galaxies about 2 billion light-years away, did not fit that pattern.

Artist’s conception of how the ‘nearly naked’ supermassive black hole originated. Image credit: Bill Saxton, NRAO / AUI / NSF.

Further studies showed that this object, labeled B3 1715+425, is a supermassive black hole surrounded by a small galactic remnant only about 3,000 light-years across.

In addition, this object is speeding away from the core of a much larger galaxy, 2MASX 17171926+4226571, leaving a wake of ionized gas behind it.

The team concluded that B3 1715+425 is what has remained of a small galaxy that passed through the larger one and had most of its stars and gas stripped away by the encounter.

The speeding galactic remnant probably will lose more mass and cease forming new stars.

“In a billion years or so, it probably will be invisible. That means that there could be many more such objects left over from earlier galactic encounters that astronomers can’t detect,” Dr. Condon said.


Gravitational Collapse is Not Self Limiting

Now consider gravitational collapse. As Newton first told us over 300 years ago, all bodies gravitationally attract all other bodies. So matter naturally wants to clump together in ever denser, smaller clumps. This process is gravitational collapse.

It is not a self-limiting process. The more matter clumps together, the stronger become the forces that drive the clumping. That is an immediate consequence of Newton's inverse square law. The gravitational force between bodies varies inversely with the square of the distance between them.

As two bodies near and the distance between them reduces from 3 to 2 to 1, the gravitational force pulling them together increases ninefold: from 1/9 to 1/4 to 1.


The same thing happens if we have a large sphere of matter collapsing gravitationally.

In short, if we have a cluster of masses that fall together under their mutual gravitational attraction, those forces of attraction will grow stronger as the masses come closer together. There is nothing in the properties of gravity to prevent the continued collapse. In this sense, gravitation forever threatens a catastrophic, runaway collapse.

So what stops it?

The process of gravitational collapse just described is the process by which stars, galaxies and planets are formed. Cosmic debris, hydrogen or other elements, coalesce under their own gravity to produce these celestial objects. What prevents their collapsing to a point? Other forces intervene.

There are three types of forces that halt continuing collapse. Each force has its limit.

Gravitational collapse of. is halted by. But that halting force can be overcome by.
Galaxies and planetary systems.
Their matter forms great, orbiting swirls as they collapse together.
The orbital motion of stars in galaxies and planets in solar systems lead to centrifugal forces that prevent the stars and planets falling to the centers of the systems If these motions are lost due to collisions, collapse can ensue.
Stars.
They become very hot as they form from gravitationally collapsing clouds of cosmic matter.
Their high temperatures yield high pressures that balance the continuing pull of gravity. Stars are radiating away their heat. Even though nuclear reactions contribute more heat, eventually they will burn out and the stars will cool.
Planets. The mechanical rigidity of the rocks and incompressibility of the molten core of rocky planets prevent further collapse. The gas pressure of gas giants prevent their collapse. If the gravitational forces are strong enough because a lot of matter is collapsing, these mechanical forces can be overcome.

The table summarizes how three different effects prevent complete gravitational collapse. The circumstances with stars needs a little more explanation.

Stars are huge spheres of gases, heated to very high temperatures by the energy released in gravitational collapse and then by thermonuclear reactions ignited by the rising temperatures. Those high temperatures cause the gases to expand. If those expanding gases were somehow trapped in a chamber so the expansion was halted, very high pressures would result. The gravitation of the star itself provides just such a chamber. The gravitational attraction of each part of the star for all other parts pulls back on the other parts, stopping the expansion and producing high pressure.

The stability of the star consists in a perfect balance of the outward pressure forces and the inward gravitational forces. It is a temporary balance, since the nuclear fuel of the stars will eventually burn out.


The Mass of Cygnus X-1

Cygnus X-1 is part of a binary system, first discovered in 1964 by its powerful X-rays. Closer inspection showed a supergiant star orbiting an unseen companion every 5.6 days. The black hole is siphoning material away from the star, releasing X-rays and radio jets in the process.

About a decade ago, scientists were able to make the first precise calculations of the system’s distance and mass using the Very Long Baseline Array (VLBA), a network of radio telescopes spread across the U.S.

“As the Earth moves around the Sun, we see Cygnus X-1 from different vantage points,” explains study lead James Miller-Jones (International Centre for Radio Astronomy Research-Curtin University, Australia). As a result, Cygnus X-1 — and the radio jet it emits — appears to move back and forth against the backdrop of far more distant galaxies. Measuring this shift enables scientists to work out the distance to the black hole and its star companion, which affects the calculation of their masses. The 2011 observations were taken over the course of a year and suggested that Cygnus X-1 is about 6,000 light-years away and 15 times the mass of the Sun.

For the current study, Miller-Jones and colleagues used the VLBA to observe the system over six days to watch how the radio emission changes over the course of a single orbit. They used this information to correct for the supergiant’s stellar wind, which absorb radio emission passing through it and can thus shift the apparent position of the black hole’s radio jet base. Combining this understanding with archival observations taken over more than seven years, the team obtained improved radio measurements.

The new results show that Cygnus X-1 is more than 7,000 light-years away and thus more massive than originally thought. The new calculations show the black hole has the mass of 21 Suns the giant star companion is around 40 solar masses. The results put the radio measurements in agreement with visible-light measurements of parallax from the European Space Agency’s Gaia satellite.


Astronomers find closest black hole yet in ‘nearby’ star system

An artist’s impression depicts the orbits of two stars (in blue) and a stellar mass black hole (in red) in a triple system just 1,000 light years from Earth. . Image: ESO/L. Calçada

Astronomers studying what they thought was a double star system 1,000 light years from Earth in the southern constellation Telescopium stumbled on what must be a stellar mass black hole, an unseen companion with four times the mass of the Sun that gravitationally shapes the orbit of its nearest companion. It is the nearest known black hole to Earth.

“We were totally surprised when we realised that this is the first stellar system with a black hole that can be seen with the unaided eye,” said Petr Hadrava, emeritus scientist at the Academy of Sciences of the Czech Republic in Prague and co-author of a study in the journal Astronomy & Astrophysics.

The star system, known as HR 6819, was observed as part of a study of binary star systems. Using the FEROS spectrograph with the European Southern Observatory’s MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile, researchers were surprised to find one of the visible stars, one with at least five times the mass of the sun, was orbiting an unseen body every 40 days. The second visible star is at a larger distance from the inner pair.

Analysing the inner star’s motion, the team concluded it is orbiting a black hole.

“This system contains the nearest black hole to Earth that we know of,” said ESO scientist Thomas Rivinius, who led the study. “An invisible object with a mass at least four times that of the Sun can only be a black hole.”

Only a few dozen stellar-mass black holes have been found in the Milky Way to date. Most of them interact violently with their environment, releasing bursts of detectable X-rays. But quiescent black holes may be a commonplace end state for massive stars across the galaxy’s history.

“There must be hundreds of millions of black holes out there, but we know about only very few,” said Rivinius. “Knowing what to look for should put us in a better position to find them.”


Earliest Known Gigantic Black Hole Storm at the Dawn of Galaxies Detected

Astronomers have observed that the farthest galaxy is still driven by air from its supermassive black hole. Light from this object came 13.1 billion years ago. This is only 670 million years after the Big Bang and 100 million years more than the previous record holder. As published in the Astrophysical Journal, the discovery was made possible by the Atacama Large Millimeter / Submillimeter Array (ALMA). The galaxy, HSC J124353.93 + 010038.5 (abbreviated J1243 + 0100) has a supermassive black hole at its center.

This is thought to be the case for almost every galaxy in the universe, and astronomers have determined the relationship between the size of a supermassive black hole and the size of its galaxies, although the scales considered are relatively different. The key to understanding the process in this connection is related to the feeding process of black holes. When enough material enters the interior of the galaxy, a supermassive black hole begins to consume large amounts of matter. This type of substance will move at high speeds emitting intense energy which may result in pushing some of the surrounding matter outwards.

This is the beginning of this galactic wind, which could lead to the formation of a new star that would change the galaxy for a long time. J1243 + 0100 is currently the first example of this type of wind. Lead author Takuma Izumi, from the National Astronomical Observatory of Japan (NAOJ), said in a statement, “The question is, when did galactic winds come into existence in the universe?”

“This is an important question because it relates to an important problem in astronomy: how did galaxies and supermassive black holes coexist?” Thanks to ALMA, the team was able to study the motion of gas in the galaxy beyond the emission of air. The mass ratio observed in this ultra-distant galaxy is similar to that observed by astronomers in the recent universe, which provided some important clues about the mechanism behind the supermassive black hole-galaxy connection.

“Our observations support recent high-precision computer simulations that predict that there was a contemporary relationship about 13 billion years ago.” “We plan to observe such a large number of objects in the future, and hopefully clarify whether the primitive covolution seen in this matter is an accurate picture of the general universe of that time.” The central region of the galaxy was estimated to be about 30 billion times the mass of the Sun, of which the black hole was about 1 percent.


Earth Faster, Closer to Black Hole in New Map of Galaxy

Position and velocity map of the Milky Way Galaxy. Arrows show position and velocity data for the 224 objects used to model the Milky Way Galaxy. The solid black lines show the positions of the Galaxy’s spiral arms. The colors indicate groups of objects belonging the same arm. The background is a simulation image. (Credit: NAOJ) Original size (3.5MB)

Earth just got 7 km/s faster and about 2000 light-years closer to the supermassive black hole in the center of the Milky Way Galaxy. But don’t worry, this doesn’t mean that our planet is plunging towards the black hole. Instead the changes are results of a better model of the Milky Way Galaxy based on new observation data, including a catalog of objects observed over the course of more than 15 years by the Japanese radio astronomy project VERA.

VERA (VLBI Exploration of Radio Astrometry, by the way “VLBI” stands for Very Long Baseline Interferometry) started in 2000 to map three-dimensional velocity and spatial structures in the Milky Way. VERA uses a technique known as interferometry to combine data from radio telescopes scattered across the Japanese archipelago in order to achieve the same resolution as a 2300 km diameter telescope would have. Measurement accuracy achieved with this resolution, 10 micro-arcseconds, is sharp enough in theory to resolve a United States penny placed on the surface of the Moon.

Because Earth is located inside the Milky Way Galaxy, we can’t step back and see what the Galaxy looks like from the outside. Astrometry, accurate measurement of the positions and motions of objects, is a vital tool to understand the overall structure of the Galaxy and our place in it. This year, the First VERA Astrometry Catalog was published containing data for 99 objects.

Based on the VERA Astrometry Catalog and recent observations by other groups, astronomers constructed a position and velocity map. From this map they calculated the center of the Galaxy, the point that everything revolves around. The map suggests that the center of the Galaxy, and the supermassive black hole which resides there, is located 25800 light-years from Earth. This is closer than the official value of 27700 light-years adopted by the International Astronomical Union in 1985. The velocity component of the map indicates that Earth is travelling at 227 km/s as it orbits around the Galactic Center. This is faster than the official value of 220 km/s.

Now VERA hopes to observe more objects, particularly ones close to the central supermassive black hole, to better characterizes the structure and motion of the Galaxy. As part of these efforts VERA will participate in EAVN (East Asian VLBI Network) comprised of radio telescope located in Japan, South Korea, and China. By increasing the number of telescopes and the maximum separation between telescopes, EAVN can achieve even higher accuracy.

“The First VERA Astrometry Catalog” by VERA collaboration et al. appeared in Publications of the Astronomical Society of Japan in August 2020.


Surprising Second Black Hole Found in Milky Way's Center

Astronomers think they have found a rare if not unique black hole very near the center of the Milky Way. That would make two of the beasts in that part of the galaxy.

The discovery also adds weight to the idea that black holes come in three sizes, essentially small, medium and large.

Stellar black holes -- the remains of collapsed stars, are common. They typically harbor as much mass as a few suns. And for years, scientists have known there are supermassive black holes in many galaxies one with the mass of more than three million suns anchors the Milky Way.

The newly detected object appears to be an intermediate mass black hole, packing about 1,300 solar masses.

Intermediate mass black holes ought to exist, some theorists say, because they should have been the building blocks of supermassive black holes. A few should be left scattered around any respectable galaxy. But attempts to discover them -- data suggest two others exist in our galaxy -- have so far proved inconclusive.

Black holes can't be seen, because everything that falls into them, including light, is trapped. But the swift motions of gas and stars near an otherwise invisible object allows astronomers to calculate that it's a black hole and even to estimate its mass.

If the newfound object, catalogued as GCIRS 13E, is indeed a middleweight black hole, it is likely a rare variety, perhaps one of kind, that formed farther out and has been lured to the galactic center. It is now less than 1.5 light-years from the fringes of the known supermassive black hole. That's much closer than our Sun is to the next nearest star.

Orbiting the presumed middleweight are seven stars, each of which in its prime was more than 40 times the mass of the Sun. Even as corpses they contain five to 10 solar masses. The whole setup is racing around the galactic center at 626,300 mph (280 kilometers per second).

Theory holds that these stars could not have formed in their present location, because the gravity of the nearby supermassive black hole wouldn't have allowed a gas cloud to contract into a star, says study leader Jean-Pierre Maillard of the Institute of Astrophysics in Paris.

On the other hand, Maillard told SPACE.com, the stars could not have formed too far from their present location. Why? Because there wasn't time. Massive stars die young. The seven examined in the study can't be more than 10 million years old, or they would have exploded already. So the seven stars, along with the middleweight black hole, all had to migrate inward within the past 10 million years -- an eyeblink in the 13 billion years of the galaxy's lifetime.

All this means the cluster probably formed about 60 light-years out beyond its current orbit, the calculations show.

Maillard said the seven stars are the remains of what likely was once a cluster of many stars. In such a globular cluster, as astronomers call it, a middleweight black hole could develop through runaway star collisions, other research has found.

"It might be unique," Maillard said of the black hole candidate. Other middleweights might exist in the galaxy, he said, but probably none so close to the center.

The study relied on data from several telescopes, including the Gemini Observatory in Hawaii and the European Southern Observatory in Chile.

There are other clues as to what's there. The location of the apparent middleweight black hole coincides with a source of X-rays noted by the Chandra X-ray Observatory. Black holes are known to create intense X-ray emissions as gas swirls inward and is superheated.

Maillard cautions, however, that more observations are needed to pin down with certainty the existence and identity of the object.

The discovery, announced last week, is detailed in the journal Astronomy and Astrophysics.


How the position of this black hole known? - Astronomy

I have read that a black hole has very strong gravitation force and nothing can escape from the gravitational force of a black hole not even light. Now my question is what is the size of the black hole?

When you read about black holes, you would have read about something called the event horizon. That is the point from which light can no longer escape from the black hole. Nobody knows as to what really happens inside the event horizon. One needs to have a theory on quantum gravity to explain that. Classically, matter collapses to a point, called a singularity (infinite density), but what really happens is not known.

When astronomers refer to the "size" of the black hole, they are talking about the event horizon. The event horizon is refers to the location from the black hole where the escape velocity equals the speed of light. In other words, no particle (even light) can escape from within the event horizon.

Mathematically, the size of the black hole is given by 2GM/c 2 where G is the gravitational constant, M is the mass of the black hole and c is the speed of light. So, when one says that the black hole has a size of 5 km, it means that the event horizon is at a distance of 5 km from the center of the black hole. If the Sun were to become a black hole, then its size would be about 3 km.

This page was last updated June 27, 2015

About the Author

Jagadheep D. Pandian

Jagadheep built a new receiver for the Arecibo radio telescope that works between 6 and 8 GHz. He studies 6.7 GHz methanol masers in our Galaxy. These masers occur at sites where massive stars are being born. He got his Ph.D from Cornell in January 2007 and was a postdoctoral fellow at the Max Planck Insitute for Radio Astronomy in Germany. After that, he worked at the Institute for Astronomy at the University of Hawaii as the Submillimeter Postdoctoral Fellow. Jagadheep is currently at the Indian Institute of Space Scence and Technology.


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