Saturday, October 2, 2021

3291 - GRAVITATIONAL LENSING - Quasars, GRBs, Blackholes?

  -  3291   -  GRAVITATIONAL  LENSING  -  Quasars, GRBs, Blackholes?  Catching the rerun of the explosive event will help astronomers measure the time delays between four supernova images.  This will offer clues as to the type of warped-space terrain the exploded star's light had to cover to reach us.


-----  3291  -  GRAVITATIONAL  LENSING  -  Quasars, GRBs, Blackholes?

-   The distant supernova, named “Requiem“, is embedded in the giant galaxy cluster “MACS J0138“. The cluster is so massive that its powerful gravity bends and magnifies the light from the supernova, located in a galaxy far behind it. 

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-  Called “gravitational lensing“, this phenomenon splits the supernova's light into multiple mirror images. 

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-   Supernovae explode and fade away over time. Researchers predict that a rerun of the same supernova will make an image appearance in 2037. The light from Supernova Requiem needed an estimated 10 billion years for its journey, based on the distance of its host galaxy.

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-   The light from the cluster took four billion years to reach Earth.  

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-  This future appearance will be the fourth-known view of the same supernova, magnified, brightened, and split into separate images by a massive foreground cluster of galaxies acting like a cosmic zoom lens. Three images of the supernova were first found from archival data taken in 2016 by NASA's Hubble Space Telescope.

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-  The multiple images are produced by the monster galaxy cluster's powerful gravity, which distorts and magnifies the light from the supernova far behind it, ie: gravitational lensing. First predicted by Albert Einstein, this effect is similar to a glass lens bending light to magnify the image of a distant object.

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-  The three lensed supernova images, seen as tiny dots captured in a single Hubble snapshot, represent light from the explosive aftermath. The dots vary in brightness and color, which signify three different phases of the fading blast as it cooled over time.

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-   The light that Hubble captured from the cluster took about four billion years to reach Earth. The light from Supernova Requiem needed an estimated 10 billion years for its journey.

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-  Dark matter is an invisible material that comprises the bulk of the universe's matter and is the scaffolding upon which galaxies and galaxy clusters are built.

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-  Each magnified image takes a different route through this cluster and arrives at Earth at a different time, due to differences in the length of the pathways the supernova light followed.

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-  Whenever some light passes near a very massive object, like a galaxy or galaxy cluster, the warping of space-time that Einstein's theory of general relativity tells us is present for any mass, delays the travel of light around that mass.

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-   The lensed supernova image predicted to appear in 2037 lags behind the other images of the same supernova because its light travels directly through the middle of the cluster, where the densest amount of dark matter resides. The immense mass of the cluster bends the light, producing the longer time delay. 

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-  The rerun of the explosive event allow astronomers to measure the time delays between all four supernova images to characterize the type of warped-space terrain the exploded star's light had to cover.

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-   Researchers can fine-tune the models that map out the cluster's mass. Developing precise dark-matter maps of massive galaxy clusters is another way for astronomers to measure the universe's expansion rate and investigate the nature of dark energy which is a mysterious form of energy that works against gravity and causes the cosmos to expand at a faster rate.

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-  There is new science behind a stunning 2020 Hubble image that illuminates behind a shining loop of light.  The circle, also called an “Einstein ring” after the famous physicist who predicted its existence, came about due to a galactic-scale illusion. 

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-  The galaxy this so-called "molten ring" curls located in the Southern Hemisphere constellation of Fornax, the Furnace.  The big ring is actually a light smear created by a lensing effect that occurs when a foreground object with strong gravity magnifies the light of a more distant galaxy behind it. 

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-   We are seeing the galaxy in the ring as it was about 9 billion years old, when the universe was only about one-third its present age of 13.8 billion years

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-  The detection of molecular gas, of which new stars are born, allowed astronomers to calculate the precise redshift and thus give confidence that we are truly looking at a very distant galaxy.

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-  Using Quasars as a new “standard candle” to define distance.    X-ray measurements of 2,332 quasars in the Chandra Source Catalog compiled by NASA’s prolific Chandra X-ray telescope, versus their luminosity in the ultraviolet as seen in the Sloan Digital Sky Survey. There is a correlation between the two factors, a correlation that extends back to quasars in the early Universe.

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-  This  relationship between X-ray and UV luminosities does not evolve with redshift and therefore it can be used with the same relation just using fluxes to compute the distance of the objects.

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-  Whatever quasars are, they’re an exotic feature of the early Universe that we don’t see in the nearby cosmos today. The first quasar discovered was 3C 273 in 1963. With a high redshift (z = 0.158) astronomers knew they were looking at something extremely distant and therefore intrinsically luminous. 

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-  “3C 273”  has an absolute magnitude value of -27.  If you placed it at a distance of 10 parsecs away, it would compete with the Sun in the sky.

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-  The first ‘rung’ on the cosmic distance ladder is “parallax“, using observations from two different points in space and basic trigonometry to gauge distance. Using the Earth’s orbit as a baseline is also the basis for the parsec which is a measure of distance, 3.26 light-years long.

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-  The next yardstick out was discovered by astronomer Henrietta Swan Levitt while examining variable stars in the Small Magellanic cloud in 1912. She noticed that a particular type of star known as a Cepheid variable pulses in a fashion that’s directly related to its luminosity. Find a Cepheid in a galaxy (as Hubble did in the Andromeda galaxy just over a decade later in 1923) and you can gauge its distance.

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-  But for larger distances, brighter standard candles are needed. For these, astronomers use Type IA supernovae, as they flare and fade in a predictable fashion. Over the immense distances of hundreds of millions of light-years, cosmic expansion and spectroscopic redshift (noted as z) comes into play.

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-   This relation is known as Hubble’s Law, it correlates velocity as proportional to distance due to the expansion of the Universe: the higher the redshift, the more distant the object.

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-  Type IA supernovae are good back to about three billion years after the Big Bang; quasars as standard candles proposed in the study would be good to just 700 million years after the Big Bang, a vast improvement.

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-  Quasars have another advantage, as hundreds of thousands of them have been discovered in recent years. As a standard candle, they provide not only a good overlap with more distant Type 1A supernovae, but are also a good backup check for distance, as they are separately distinct cosmological processes.

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-   You can, with  dark skies, observe quasar 3C 273 from your driveway with a good-sized telescope. At magnitude +12.9 it won’t look like much more than a nondescript faint star You are seeing photons that left their source 2.4 billion years ago.

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- Gamma-ray bursts (GRBs) are the brightest, most energetic blasts of light in the universe. Released by an immense cosmic explosion, a single GRB is capable of shining about a million trillion times brighter than Earth's sun.

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-  Part of the problem is that all known GRBs come from very, very far away, usually billions of light-years from Earth. Sometimes, a GRB's home galaxy is so far-flung that the burst's light appears to come from nowhere at all, briefly blipping out of the black, empty sky and vanishing seconds later. 

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-   All those nebulous empty-sky bursts could be the results of massive stellar explosions in the disks of distant galaxies.

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-  Astronomers favor two leading explanations for the empty-sky gamma-ray mystery. In one explanation, the rays occur when gas falls into the supermassive blackholes that sit at the centers of all galaxies in the universe. In this scenario, as gas particles get sucked into the blackhole, a small fraction escape and instead radiate in large, near-light-speed jets of matter. It's thought that these powerful jets could be responsible for gamma-ray bursts.

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-  The other explanation points to stellar explosions called supernovas. When large stars run out of fuel and erupt in these violent supernovas, they can send nearby particles blasting away at near-light speed. These highly energetic particles, called cosmic rays, may then collide with other particles sprinkled through the gassy hinterland between stars, producing gamma-rays.

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-  Blackholes are probably still responsible for some of the gamma-rays that our satellites pick up, the researchers added. But when it comes to the mysterious empty-sky GRBs, the hungry holes are simply not necessary; exploding stars in faraway corners of the universe are sufficient to explain the phenomenon. 

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-  October 2, 2021    GRAVITATIONAL  LENSING  -  Quasars,      3291                                                                                                                                                    

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--------------------- ---  Saturday, October 2, 2021  ---------------------------






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