NASA supports event Horizon Telescope to study Milky Way’s Black Hole

(ORDO NEWS) — The black hole at the center of our galaxy has been the subject of a groundbreaking new image from a collaboration between the Event Horizon Telescope.

As the Event Horizon telescope collected data for a stunning new image of the Milky Way’s supermassive black hole, a legion of other telescopes watched, including NASA’s three X-ray observatories in space.

Astronomers are using these observations to learn more about how the black hole at the center of the Milky Way galaxy – known as Sagittarius A* (Sgr A* for short) – interacts with and feeds on its environment some 27,000 light-years from Earth.

When the Event Horizon Telescope (EHT) observed Sgr A* in April 2017 to take a new image, the scientists from the collaboration also looked at the same black hole with equipment that detects different wavelengths of light.

As part of this multi-wavelength observing campaign, they collected X-ray data from NASA’s Chandra X-ray Observatory, the NuSTAR Nuclear Spectroscopic Telescope, and Neil Gehrels’ Swift Observatory; radio data from the East Asian Very Long Baseline Interferometer (VLBI) network and the global 3 mm VLBI network; infrared data from the European Southern Observatory’s Very Large Telescope in Chile.

The Event Horizon Telescope has taken another remarkable image, this time of the giant black hole at the center of our home galaxy,” said NASA Administrator Bill Nelson.

“Better looking at this black hole will help us learn more about its cosmic impact on the environment and is an example of international cooperation that will take us into the future and open up discoveries that we could never have imagined.”

One important goal was to capture X-ray flares, which are thought to be driven by magnetic processes similar to those seen on the Sun but could be tens of millions of times more powerful.

These flares occur roughly daily in the region of the sky observed by the EHT, a region slightly above the event horizon of Sgr A*, the point of no return for infalling matter.

Another goal was to get a critical look at what is happening on a larger scale. While the EHT results show striking similarities between Sgr A* and the previous black hole M87*, the bigger picture is much more complex.

“If the new EHT image shows us the eye of a black hole hurricane, then these multi-wavelength observations show winds and rain equivalent to hundreds or even thousands of kilometers beyond,” said Daryl Haggard of McGill University in Montreal, Canada, one of the lead scientists. “How does this cosmic storm interact with and even destroy the galactic environment?”

One of the biggest questions about black holes is how exactly they collect, absorb, or even eject material orbiting them at near-light speeds, in a process known as “accretion.” This process is fundamental to the formation and growth of planets, stars, and black holes of all sizes throughout the universe.

Chandra’s images of the hot gas around Sgr A* are critical to the study of accretion, as they allow us to determine how much material is captured by the black hole’s gravity from nearby stars, as well as how much material has time to reach the event horizon.

This crucial information is not available with modern telescopes for any other black hole in the universe, including M87*.

“Astronomers basically agree that black holes have material spinning around them, and some of it is forever falling below the event horizon,” says Sera Markoff of the University of Amsterdam in the Netherlands, another coordinator of multiwavelength observations. “With all the data we’ve collected for Sgr A*, we can go a lot further than this basic picture.”

Scientists in a major international collaboration compared data from NASA’s high-energy missions and other telescopes with state-of-the-art computational models that take into account factors such as Einstein’s general theory of relativity, the effects of magnetic fields, and predictions of how much radiation matter around a black hole should generate at different wavelengths.

Comparison of models with measurements gives hints that the magnetic field around the black hole is strong and that the angle between the black hole’s line of sight and its axis of rotation is small, less than 30 degrees.

If confirmed, this means that from our vantage point we are looking down on Sgr A* and its ring is larger than it is from the side, which is remarkably similar to the first EHT target, M87*.

“None of our models fit the data perfectly, but now we have more specific information to work with,” said Kazuhiro Hada of Japan’s National Astronomical Observatory. “The more data we have, the more accurate our models and ultimately our understanding of black hole accretion will become.”

During the EHT observations, the researchers also managed to capture X-ray flares or bursts from Sgr A*: faint, observed with Chandra and Swift, and moderately bright, observed with Chandra and NuSTAR. X-ray flares similar in brightness to the latter are regularly observed at Chandra, but this is the first time the EHT has simultaneously observed Sgr A*, providing an exceptional opportunity to determine the responsible mechanism from real images.

The intensity and variability of millimeter waves observed with the EHT increase within hours immediately after the brighter X-ray burst, which was not observed in millimeter observations a few days earlier. Analysis and interpretation of EHT data obtained immediately after the outbreak will be presented in future publications.


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