3480 - MILKY WAY - mysterious center of our galaxy? Discovering the center of the Milky Way Galaxy all began all began with the discovery of Sagittarius A*, a persistent radio source located at the Galactic Center of the Milky Way that turned out to be a supermassive blackhole (SMBH).
------------- 3480 - MILKY WAY - mysterious center of our galaxy?
- This discovery was accompanied by the realization that the blackhole exist at the heart of most galaxies, which account for their energetic nature and the hypervelocity jets extending from their center. Since then, scientists have been trying to get a better look at Sag A* and its surroundings to learn more about the role blackholes play in the formation and evolution of our galaxy.
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- This has been the goal of the GRAVITY collaboration of astronomers that have been studying the core of the Milky Way for the past thirty years. Using the ESO’s Very Large Telescope Interferometer (VLTI), this team obtained the deepest and sharpest images to date of the region around Sag A*.
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- These observations led to the most precise measurement yet of the blackhole’s mass and revealed a never-before-seen star that orbits close to it.
This unique instrument combines the light of all four 8.2-meter (27 ft) telescopes at the Very Large Telescope’s (VLT) located at the Paranal Observatory in Chile – a technique known as interferometry.
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- The Milky Way, Sagittarius A*: How massive is it exactly? Does it rotate? Do stars around it behave exactly as we expect from Einstein’s general theory of relativity?
The atronomers were using a machine-learning technique called “Information Field Theory“. This consisted of modeling how the real light sources would appear, how GRAVITY would observe them, then comparing the simulated results to the actual observations. This allowed them to acquire highly-accurate measurements of Sag A* and images of Galactic Center that were 20 times sharper than any made by the individual VLT telescopes alone.
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- Images obtained by the GRAVITY instrument between March and July 2021, showed stars orbiting very close to Sgr A*, the supermassive black hole at the heart of the Milky Way. This included “S29“, which holds the record for making the closest and speediest approach around Sag A* ever observed.
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- This star , “S29” made its nearest pass in late May 2021, passing within 8 billion miles, or 90 times the distance between the Earth and Sun (90 AU) – and achieving a velocity of 8,740 km per second (5,430 miles per second).
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- The VLTI gives us this incredible spatial resolution, and with the new images, we reach deeper than ever before. We are stunned by their amount of detail, and by the action and number of stars they reveal around the black hole.
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- Following stars on close orbits around Sagittarius A* allows us to precisely probe the gravitational field around the closest massive blackhole to Earth, to test General Relativity, and to determine the properties of the blackhole.
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- Originally proposed by Albert Einstein in 1916, General Relativity provides a geometric explanation of gravitation and its effect on space-time. Since then, scientists have sought opportunities to test this theory under the most extreme conditions, which super massive blackholes provide.
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- These latest observations confirmed that the stars follow paths predicted by General Relativity perfectly. From this, the team was able to constrain the mass of Sag A* to 4,300,000 Solar Masses.
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- The distance to Sagittarius A* -------- 27,000 light-years from Earth.
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- Further observations of the Galactic Center will be possible in the coming years as the GRAVITY instrument is upgraded with the installation of GRAVITY+. This upgrade will push the sensitivity of the VLTI even further and reveal fainter stars that orbit even closer to Sag A*.
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- The team aims to eventually find stars that orbit so close to Sag A* that they are subject to the gravitational effects caused by the blackhole’s rotation.
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- The Extremely Large Telescope (ELT) in the Atacama Desert in northern Chile. Once it is complete by 2027, the ELT will be the most powerful observatory in the world and allow for the most precise measurements of these stars’ velocities. It will be joined by the Giant Magellan Telescope (GMT), which is scheduled for completion by 2025.
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- Thee inner 600 light years of our galaxy is a maelstrom of cosmic radiation, turbulent swirling gas clouds, intense star formation, supernovae, huge bubbles of radio energy, and of course this giant supermassive blackhole.
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- The new “MeerKAT” image of the Galactic center region is shown with the Galactic plane running horizontally. MeerKAT is located in South Africa which has a vantage point of the galaxy’s center 25,000 light years away toward the constellation Sagittarius.
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- MeerKAT sees the Universe in radio waves which penetrate interstellar dust normally obscuring this region of space. An image is the result of 144 hours of telescope observation and 70 terabytes of raw data. Created from 20 separate pointings, the image is a mosaic representing 6 square degrees of sky, the equivalent of 30 full Moons spanning 4 full Moons wide. If your eyes were sensitive enough to radio waves, this is what the galaxy would look like above you.
- The Milky Way is a flat disk of hundreds of billions of stars with a bulging central core. Within the core exists a region called the “Central Molecular Zone” or CMZ with gas densities and turbulence 10-1000 times what you find in outer disk of the Milky Way and cosmic radiation levels equally higher than the rest of the galaxy.
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- Clusters of young massive stars are being created from fresh gas drawn toward the CMZ. Some of these massive stars have already exploded in these clusters as supernovae.
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- Much of what we’re observing in the heart of the galaxy are familiar objects, stars exploding and gas flowing, but, there are mysterious structures unique to this region we don’t fully understand.
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- Reaching out from the Milky Way’s core are giant magnetic tendrils, like strands or filaments, up to 150 light years in length. They appear in pairs or clusters like “strings on a harp” separated from each other by about 1 AU (the Earth’s distance from the Sun), and act like wires conducting electrons accelerated to near the speed of light.
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- MeerKAT’s new image has uncovered 1000 more filaments – 10 times more than previously known. The filaments are difficult to see as they blend into the rest of the other structures and shapes of turbulent gas and star forming regions at the center of the galaxy.
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- Because the filaments are magnetic, the flow of electrons along their length creates a unique signature of radiation that can be detected by MeerKAT, Synchrotron radiation.
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- Synchrotron radiation is generated by the motion of high speed electrons through a magnetic field. This unique radiation allows the filaments to be teased out in images from other structures.
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- What are these filaments, what is accelerating electrons along their length, and why are they unique to the center of the galaxy?
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- Lurking at the centre of the Milky Way is a supermassive blackhole. Blackholes come in a different varieties: Supermassives weigh in at millions or even billions of times the mass of our Sun and are typically found in the centers of galaxies.
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- Extending outward from the central region of the Milky Way are two large bubbles of gas emitting radio waves. They are symmetrical, forming an hourglass rising above and below the galactic plane. This cirrus cloud-like emission from the Galactic center super bubble. This is traversed by a complex of many parallel filaments.
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- MeerKAT found these radio bubbles in 2018 which extend a thousand light years outward from the central region and are thought to be created by a massive outburst from our blackhole about 100,000 to a million years ago. It was powerful enough to send two bubbles surging outward from the galaxy’s disk. While large black holes feed, huge amounts of energy are released that could create bubbles like these.
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- There have also been outbursts of energy from the supernovae explosions and star formation in this region. It’s possible the filaments are created by the interaction of both the radio bubbles and star formation as the magnetic fields of energized gases expanding from the blackhole become entangled with outbursts from stellar formation and explosions. The blackhole’s outbursts also accelerate electrons along the length of the filaments themselves.
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- If an interaction between the blackhole outbursts and supernova explosions creates the filaments, that interaction would explain why the filaments are unique to this part of the galaxy. They also seem to appear only within the radio bubbles themselves.
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- The filaments have also captured cosmic rays, high energy particles created by stars, in their magnetic fields. The particles can be dated essentially leaving a time stamp on the filaments. The MeerKAT images make it possible to catalogue each of the filament clusters to learn more about them and therefore the story of the center of our galaxy.
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- As the gas approaches the black hole, it is heated beginning to ionize where electrons are stripped from the gas. The ionized gas appears as a “mini-spiral” within five light years of the central blackhole. This cloud of ionized gases and synchrotron radiation swirling about our black hole is light years across.
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- In the early 1930’s astronomer Karl Jansky first detected radio emission from the galactic center. That observation, considered the birth of radio astronomy, was the earliest version of what MeerKAT is observing now. It’s possible some of those radio emissions Jansky detected were the first observation of the blackhole at the center of our galaxy.
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- We’ve come a ways since Jansky’s radio telescope built literally on Ford Model-T wheels. Inaugurated in 2018 with 64 antennae spread over 8 kilpmeters of the Northern Cape of South Africa, MeerKAT is the most sensitive radio telescope of its kind. Bet
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- This unprecedented new telescope image of the Milky Way galaxy's turbulent center has revealed nearly 1,000 mysterious strands dangling in space. Stretching up to 150 light years long, the one-dimensional strands (or filaments) are found in pairs and clusters, often stacked equally spaced, side by side like strings on a harp.
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- Using observations at radio wavelengths astronomers discovered the highly organized, magnetic filaments in the early 1980s. The mystifying filaments comprise cosmic ray electrons gyrating the magnetic field at close to the speed of light. But their origin has remained an unsolved mystery ever since.
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- Now, the new image has exposed 10 times more filaments than previously discovered, enabling astronomers to conduct statistical studies across a broad population of filaments.
Astronomers finally see the big picture, a panoramic view filled with an abundance of filaments.
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- To construct the image with unprecedented clarity and detail, astronomers spent three years surveying the sky and analyzing data at the South African Radio Astronomy Observatory (SARAO). Using 200 hours of time on SARAO's MeerKAT telescope, researchers pieced together a mosaic of 20 separate observations of different sections of the sky toward the center of the Milky Way galaxy, 25,000 light years from Earth.
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- Along with the filaments, the image captures radio emissions from numerous phenomena, including outbursting stars, stellar nurseries and new supernova remnants.
The filaments are related to past activity of the Milky Way's central supermassive black hole rather than coordinated bursts of supernovae. The filaments also could be related to enormous, radio-emitting bubbles.
Astronomers can find the strength of magnetic fields, their lengths, their orientations and the spectrum of radiation. But among the remaining mysteries is how structured the filaments appear. Filaments within clusters are separated from one another at perfectly equal distances, about the distance from Earth to the sun.
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- These filaments almost resemble the regular spacing in solar loops. We still don't know why they come in clusters or understand how they separate, and we don't know how these regular spacing’s happen. Every time we answer one question, multiple other questions arise. They still don't know whether the filaments move or change over time or what is causing the electrons to accelerate at such incredible speeds.
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- Astronomers are currently identifying and cataloging each filament. The angle, curve, magnetic field, spectrum and intensity of each filament. Understanding these properties will give the astrophysics community more clues into the filaments' elusive nature.
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February 26, 2022 MILKY WAY - mysterious center of our galaxy? 3480
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