- 2928 - MILKY WAY GALAXY - precision mapping? The most precise 3-D map of our Milky Way galaxy in the year 2020 has been produced by astronomers. This 3-D Milky Way map was created using data from the European Space Agency’s “Gaia space probe” that’s been scanning the stars since 2013.
------------------ 2928 - MILKY WAY GALAXY - precision mapping?
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- This new Gaia map allows astronomers to measure acceleration and to find out how much the universe has expanded since the dawn of time
- An impressive 1,800,000,000 stars are featured on the map, give or take a couple. The new Gaia data have allowed astronomers to trace the various populations of older and younger stars out towards the very edge of our galaxy, called the galactic anti-center.
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- Computer models predicted that the disc of the Milky Way will grow larger with time as new stars are born. The new data allow us to see the relics of the 10 billion-year-old ancient disc and so determine its smaller extent compared to the Milky Way’s current disc size.
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- This new 3D map was revealed that Earth is closer to the black hole at the centre of our galaxy than previously thought. The Milky Way has a huge black hole at the centre called Sagittarius A*.
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- Back in 1985, Earth was thought to be 27,700 light years away from Sagittarius A*. The new map puts it at 25,800 light-years away. One light year works out at about six trillion miles.
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- Earth just got 7 km/s , (15,660 miles per hour), faster and about 2,000 light-years closer to the supermassive black hole in the center of the Milky Way Galaxy.
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- VERA (VLBI ‘Exploration of Radio Astrometry“, "VLBI" stands for “Very Long Baseline Interferometry‘) started in 2,000 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 2,300 kilometer diameter telescope would have.
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- 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.
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- “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. In 2020, the First VERA Astrometry Catalog was published containing data for 99 astronomical objects.
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- From the position and velocity map astronomers calculated the center of the Galaxy, the point that everything revolves around. The map suggests that the center of the Galaxy, and the supermassive blackhole which resides there, is located 25, 800 light-years from Earth.
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- This is closer than the previous official value of 27,700 light-years adopted by the International Astronomical Union in 1985. The velocity component of the map indicates that Earth is traveling at 227 km/s ( 508,000 miles per our) as it orbits around the Galactic Center. This is faster than the official value of 220 km/s.( 494,000 miles per hour)
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- 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.
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- A galaxy like the Milky Way, light comes entirely from a combination of shining stars and glowing gas. However, in an active galaxy, the energy output is too high to attribute to these factors alone. The excess energy is concentrated in the galaxy’s center, the active galactic nucleus. That started the search for a blackhole at the center.
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- Active galactic nuclei (AGN) are found throughout the cosmos in many forms. Some hide within seemingly normal galaxies, while the brightest pump out so much energy they outshine their host galaxy entirely.
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- AGN are manifestations of the supermassive blackholes found in nearly every galaxy we see, and they have played an important role in shaping the universe. Observations of galactic centers had turned up odd results since the early 1900s, but initially received little attention.
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- By the late 1950s, astronomers surveying the sky with radio telescopes were attempting to match radio sources with visible objects such as stars and galaxies. They discovered that while many optical counterparts were normal-looking galaxies, some appeared as bright blue stars often embedded in fuzzy halos barely discernible in the wash of light from the star.
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- These oddballs, initially dubbed “radio stars” and later “quasi-stellar radio sources,” or “Quasars” remained mysterious until 1963, when Dutch astronomer Maarten Schmidt observed the star like counterpart of radio source 3C 273 from Palomar Observatory in California. He examined the source’s spectra, spreading out the light by wavelength to identify features associated with the emission and absorption of energy by different atoms.
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- The unified model of AGN states that all AGN contain the same components, simply viewed at different angles. From the inside out, AGN contain a supermassive blackhole; an accretion disk and a hot corona of gas; a fast-moving gas region; an obscuring torus of dust; and a slower-moving gas region. Some AGN have powerful jets, which may be pointed toward Earth.
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- Astronomers recognized a series of features associated with hydrogen, as if the features had been shifted as a group to redder wavelengths. This phenomenon, called “redshift“, occurs when an object recedes at great speeds, causing the wavelength of its light to shift toward the red end of the spectrum.
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- The hydrogen lines observed had been shifted by an amount corresponding to a redshift of 0.158, placing 3C 273 roughly 2 billion light-years away. But if the 13th-magnitude “star” really was so distant, it must be shining at least 100 times brighter than a normal galaxy.
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- Shortly afterward, astronomers revisited the spectrum of a different radio star, 3C 48, and identified features associated with a redshift of 0.3679, corresponding to a distance of over 4 billion light-years.
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- Measurements of more quasi-stellar objects followed, all extremely distant. Soon after, the term “quasar” was coined. By 1973, astronomers had concluded that all quasars occur in the nuclei of giant galaxies. They appear “star like” because they are so bright that the galaxy around them cannot be easily seen.
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- Not all AGN are so dramatic. In 1943, Carl Seyfert reported several nearby, normal-looking spiral galaxies with unusually bright nuclei. Their centers displayed high-energy emission that could not come from stars. Galaxies like these are now called “Seyfert galaxies“; their AGN are only a fraction of the host galaxies’ total light.
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- Many AGN emit X-rays, showing up in surveys of those wavelengths. Astronomers also find AGN shining in infrared light, as their high-energy emission is absorbed by dust and re-emitted at longer wavelengths.
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- 3C 273, the first identified quasar, is so bright that it appears as a blue star. Although the quasar resides in the center of a massive elliptical galaxy, it outshines its host, rendering it invisible. A jet from the quasar, stretches 200,000 light-years.
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- Most active galaxies are variable, so astronomers can discover them by taking images of the same region of sky some time apart. Their visible light flickers over months or years, while their X-ray emission can vary over hours or days.
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- Changes on these short timescales narrow down both the mechanism powering the AGN and the size of the region they can occupy, allowing researchers to answer one key question: What powers them?
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- After the discovery of 3C 273, astronomers introduced ideas for power sources that included bursts of star formation or supernovae, and exotic options such as supermassive stars, huge pulsars, or supermassive black holes.
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- In 1969, Donald Lynden-Bell showed that the gravitational potential energy around a blackhole with a mass of 10 billion Suns and squeezed into a space 10 light-hours across could more than account for the energy outputs of quasars. He argued that matter falling at varying rates into blackholes with a range of masses could explain all AGN, from low-energy Seyfert galaxies to high-energy quasars.
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- Astronomers now believe supermassive blackholes reside in the centers of nearly all galaxies. Accretion onto these blackholes is the “central engine” powering AGN. Infalling matter forms a swirling accretion disk as it approaches the blackhole.
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- As material moves from the outer disk toward the event horizon, its gravitational potential energy is converted into radiation across the spectrum. Not all galaxies are considered active, even if the blackhole is feeding. But if there’s enough accretion, we see an AGN.
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- The brightest AGN that produce gamma rays and cosmic rays are called “Blazars” quasars with jets pointed at Earth . In 2018, researchers with the IceCube collaboration traced neutrinos and gamma rays to the blazar TXS 0506+056. The find confirmed the theory that AGN can produce high-energy neutrinos.
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- What turns the blackhole engine on? As galaxies assemble and form stars, there is a wealth of material in the core available to feed the blackhole, fueling a quasar. Over time, however, that fuel runs out, and the quasar shuts off. Compared with the lifetimes of galaxies, the “active” lifetime of a quasar is short and occurs early in the galaxy’s development.
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- Even after being turned off, AGN can be reactivated if interactions, galaxy mergers, or close flybys, funneling material inward toward the supermassive black hole, restarting accretion.
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- The evolution of quasars and the evolution of galaxies look very similar, and they’re actually very closely linked. The largest number of quasars is found at the same time most galaxies in the universe were forming the bulk of their stars, between redshifts 2 and 3. There are no quasars closer than 600 million light-years, meaning none still exist today. Closer AGN are not quasars, but lower-luminosity “Seyfert galaxies“.
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- A unified theory of AGN explains their different properties through orientation effects. It states that all AGN are the same type of object viewed from different angles, and all share similar features, whether they are visible or not.
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- Every active galactic nucleus begins with a supermassive blackhole, typically defined as an object with 1 million solar masses or more. Its “event horizon” is light-hours across. Just above it is the accretion disk and a hot, spherical corona of gas. These stretch a few light-days across. At a distance of about 100 light-days is a region of fast-moving gas.
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- About 100 light-years out, the AGN is surrounded by a torus, a doughnut-shaped ring of dust and gas that can hide portions of the central engine from view, depending on the angle it tilts with respect to Earth. Beyond the torus, about 1,000 light-years out, is a region of smaller slower-moving gas clouds.
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- Astronomers obtain a spectrum to look for features associated with emission or absorption of energy by atoms. The spectrum of the quasar CXOCDFS J033229.9-275106 has a redshift of 3.6, placing it about 12 billion light-years away.
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- One of the quasar’s strongest features is the Lyman-alpha (Lyα) line, which is associated with hydrogen. In an object at rest, Lyα emission occurs at a wavelength of 121.567 nanometers; in this quasar, that wavelength has been redshifted to nearly 580 nm.
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- Some AGN have fast-moving jets, which are thought to arise from magnetic fields close to the blackhole. The jets can stretch outward for hundreds or even thousands of light-years, spewing material at close to the speed of light.
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- The angle at which we see AGN determines their classification. Looking directly down the barrel of the jet reveals a “blazar“. The two major classes of Seyfert galaxies differ only by whether both the fast- and slow-moving gas clouds can be seen, or if the torus hides the former.
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- Astronomers believe brightness does stem from intrinsic properties, including the amount of fuel available and the rate at which the black hole consumes that fuel. Different accretion modes, or types of accretion, are believed to generate more or less radiation, accounting for the range observed.
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- There are accretion modes that produce a lot of luminosity at high energies in the visible, X-ray, ultraviolet, and then there are other accretion modes that can accrete a fair amount of matter but not have a strong radioactive signature.
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- The discovery of supermassive blackholes inside galaxies brought other revelations. The mass of a galaxy’s supermassive blackhole is correlated with certain properties of the galaxy’s central regions, such as its total mass and the velocities of stars in the bulge. These links suggest that galaxies and their supermassive blackholes form and evolve together, somehow affecting each other despite their vast difference in scales.
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- Active galaxies often emit X-rays. This Chandra X-ray Observatory image of the galaxy cluster CL 0542-4100 shows hot, diffuse gas in the cluster’s center; circled points identify active galaxies within the cluster.
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- One of the things we learned about the evolution of massive galaxies is in order to reproduce the properties we see, the stellar ages, the key is not so much getting the star formation to turn on, but turning it off, and turning it off fairly abruptly and fairly early so the galaxies age quickly enough and the ellipticals look essentially like dead sources.
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- AGN feedback is one possible way to shut off star formation. Winds or jets from AGN inject energy into the galaxy’s center, heating the gas so it cannot collapse and form stars. This can pretty rapidly and quite globally in a sense shut down star formation throughout a massive galaxy.
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- How such massive blackholes form in the first place is perhaps the biggest unanswered question surrounding AGN and galaxy formation to date. Nearly all galaxies have massive black holes in their centers, and that there’s roughly a fixed fraction of the galactic bulge mass in the blackhole mass.
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- And then it makes sense that galaxies and blackholes, or galaxies and AGN, co-evolve. But it begs the question, then, of which came first: the blackhole in the center of the galaxy, or the galaxy and then the blackhole formed. So that’s one of the frontiers.
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- Active galaxies have changed the way astronomers think about the universe and the way galaxies within it grow. Their bright beacons have shaped the cosmos and still serve as powerful tools for understanding its properties across time.
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- Researchers can now explore the best-yet map of the Milky Way, with detailed information on the positions, distances and motion of 1.8 billion cosmic objects, to help us better understand our place in the universe.
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- Gaia data is like a tsunami rolling through astrophysics. This data has produced "a revolution" in many fields of astrophysics, from the study of galactic dynamics like stellar evolution to the study of nearby objects like asteroids in the solar system.
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- Gaia launched in December 2013 to map the galaxy in unprecedented detail. The $1 billion spacecraft orbits the Lagrange-2, or L2, point, a spot about 1 million miles (1.5 million kilometers) away from Earth, where the gravitational forces between our planet and the sun are balanced and the view of the sky is unobstructed.
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- Gaia can measure about 100,000 stars each minute, or 850 million objects each day, and can scan the whole sky about once every two months. The latest trove of data improves upon the precision and scope of the two previous Gaia data sets, which were released in 2016 and 2018.
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- For example, compared to the 2018 data, which included measurements for 1.7 billion objects, the 2020 data improves by a factor of two the accuracy of the data points for proper motion, or the apparent change in the position of a star as viewed from our solar system.
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- Data from Gaia has already been used across a wide range of applications over the past four years. The mission has helped researchers find the corpse of a galaxy that the Milky Way cannibalized 10 billion years ago, spot 20 hypervelocity stars unexpectedly zooming toward the galactic center, and identify about 1,000 nearby stars where hypothetical extraterrestrials would be able to see signs of life on Earth.
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- Closer to home, the spacecraft has allowed scientists to find previously unknown asteroids, and its precise data even allowed NASA to make a crucial, last-minute adjustment to the path of its New Horizons probe in 2018 to successfully swing past the icy rock Arrokoth, the most distant and primitive object in the solar system ever visited by a spacecraft.
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- The image at he beginning f this review shows the paths of 40,000 stars located within 326 light-years of our solar system over the next 400,000 years based on measurements and projections from the European Space Agency's Gaia spacecraft.
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- These super precise tests of the way masses are distributed and accelerated are essential for "probing the limits of fundamental physics. Such measurements might help scientists understand the nature of the dark matter that we know is lurking throughout the universe.
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- Even our own sun is moving so fast that our whole Milky Way would fly apart if it wasn't held together by the dark matter, and we've got no idea what the dark matter is. The hope is that by continuing experiments along the line that we're doing, making them more precise, and doing them on different scales, we'll be able to see if there are different types of dark matter.
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- The third Gaia data set was set to be released in 2022, but the mission scientists decided to release preliminary data now so astronomers could use it sooner, with at least two more data sets to be released in the coming years. The spacecraft will operate until at least 2022, but its mission may be extended until 2025
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- December 6, 2020 MILKY WAY GALAXY mapping? 2928
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