Friday, March 3, 2023

3898 - RADIO WAVES - are “light” for new telescopes.

 

-  3898  -   RADIO WAVES  -  are “light” for new telescopes.  Astronomers capture a radio signal from ancient galaxy at a record-breaking distance.  The signal was detected at a special and significant wavelength known as the "21-centimeter line" or the "hydrogen line," which is emitted by neutral hydrogen atoms.


--------------  3898  -  RADIO WAVES  -  are “light” for new telescopes.

-   The radio signal from the star-forming galaxy  ”SDSSJ0826+5630” was emitted when our 13.8 billion-year-old galaxy was just 4.9 billion years old. The signal allowed the astronomers to measure the galaxy's gas content and find that its mass is double that of the early galaxy's visible stars.

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-   Galaxies emit electromagnetic radiation, or light, across a wide range of radio wavelengths, but 21-cm-wavelength radio waves have only been seen from nearby and thus more recent galactic sources.

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-    This is the equivalent to a look-back in time of 8.8 billion years.  As the Universe expands the light waves get stretched out to where we see them as radio waves.   The difficulty in spotting these wavelengths from more distant galaxies is due to the fact that as electromagnetic radiation from early galaxies travels vast distances to Earth, the expansion of the universe stretches its wavelength and causes its energy to reduce.

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-  That means telescopes here on Earth need a natural boost to see long-wavelength, low-energy radio waves like the hydrogen line signal.

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-    General relativity suggests that objects with mass warp spacetime similar to how a ball placed on a stretched rubber sheet would weigh it down in the center, and just like in that analogy, the greater the mass, the more extreme the curvature.

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-    That means a tremendously massive object like a black hole or galaxy causes extreme curvature in spacetime just as a bowling ball would cause the extreme curvature of the rubber sheet in the analogy.

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-    This curving of spacetime causes light to bend as well as it passes by objects of tremendous mass. A phenomenon known as “gravitational lensing” occurs when a foreground or lensing object of tremendous mass sits between an observer and a background source, causing the light from the background object to curve and take different paths through and around the lensing object. This can not only make a single object appear at multiple points in the sky, but it can also have the effect of magnifying this light.

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-    This could open up a new way of using “long-wavelength radio telescopes” to probe the evolution of stars and galaxies and how the early universe evolved into the cosmos we see around us in its current era.

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-    In 1979, astronomers spotted two nearly identical quasars that seemed close to each other in the sky. These so-called “Twin Quasars” are actually separate images of the same object.   The light paths that created each image traveled through different parts of the cluster.

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-    One path took a little longer than the other. That meant a flicker in one image of the quasar occurred 14 months later in the other. The reason? The cluster’s mass distribution formed a lens that distorted the light and drastically affected the two paths.

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-    In 2022,  astronomers reported a similar effect with another distant quasar. They spent fourteen years measuring an even longer time delay between multiple images of this target quasar.

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-   The combo of galaxies and dark matter in the cluster is really entangling the quasar light as it passes through. That’s causing the light to travel different trajectories through the gravitational lens. The result is the same strange time-delayed effect.

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-    The four images of the quasar that we observe actually correspond to a single quasar whose light is curved on its path towards us by the gravitational field of the galaxy cluster.  Since the trajectory followed by the light rays to form each image is different, we observe them at different instants of time.  We have to wait 6.73 years for the signal we observed in the first image to be reproduced in the fourth one.

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-    The Sloan Digital Sky Survey first discovered cluster “SDSS J1004+4112”. Hubble Space Telescope imaged it in 2006. It was the first image of a single quasar with its light split into five images by lensing.

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-    Galaxy clusters are astonishingly massive and the largest gravitationally bound structures we know of in the universe. Some contain thousands of galaxies. The combined gravity of the galaxies, plus the intermingled dark matter in the cluster can entangle light from more distant objects as it passes through or near the cluster. It turns out that the mass of all the “stuff” in the cluster is spread out unevenly. That can affect the path of light through the cluster.

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-    Measuring these time delays helps to better understand the properties of galaxies and clusters of galaxies, their mass, and its distribution, in addition to providing new data for the estimation of the Hubble constant for the expansion rate for the Universe.  New light curves for the four bright images occurred over 14.5 years at the 1.2-meter telescope.

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-    A glowing blob known as "the cocoon," which appears to be inside one of the enormous gamma-ray emanations from the center of our galaxy dubbed the "Fermi bubbles," has puzzled astronomers since it was discovered in 2012.

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-    The “cocoon” is caused by gamma rays emitted by fast-spinning extreme stars called "millisecond pulsars" located in the Sagittarius dwarf galaxy, which orbits the Milky Way.  Thankfully for life on Earth, our atmosphere blocks gamma rays. These are particles of light with energies more than a million times higher than the photons we detect with our eyes.

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-    Because our ground-level view is obscured, scientists had no idea of the richness of the gamma-ray sky until instruments were lofted into space. But, starting with the discoveries made by the Vela satellites put into orbit in the 1960s to monitor the Nuclear Test Ban, more and more of this richness has been revealed.

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-    The state-of-the-art gamma-ray instrument operating today is the “Fermi Gamma Ray Space Telescope', a large NASA mission in orbit for more than a decade. Fermi's ability to resolve fine detail and detect faint sources has uncovered a number of surprises about our Milky Way and the wider universe.

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-    One of these surprises emerged in 2010,  something in the Milky Way's center is blowing what look like a pair of giant, gamma-ray-emitting bubbles. These completely unanticipated "Fermi bubbles" cover fully 10% of the sky.

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-   A prime suspect for the source of the bubbles is the galaxy's resident supermassive black hole. This black hole, 4 million times more massive than the Sun, lurks in the galactic nucleus, the region from which the bubbles emanate.

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-    Most galaxies host such giant black holes in their centers. In some, these black holes are actively gulping down matter. Thus fed, they simultaneously spew out giant, outflowing "jets" visible across the electromagnetic spectrum.

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-     Astronomers found this structure has nothing to do with the Fermi bubbles or, indeed, the galaxy's supermassive black hole.  Rather, they found the cocoon is actually something else entirely: gamma rays from the Sagittarius dwarf galaxy, which happens to be behind the southern bubble as seen from the position of Earth.

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-   The Sagittarius dwarf, so called because its sky position is in the constellation of Sagittarius, is a "satellite" galaxy orbiting the Milky Way. It is the remnant of a much larger galaxy that the Milky Way's strong gravitational field has literally ripped apart.  Stars pulled out of the Sagittarius dwarf can be found in "tails" that wrap around the entire sky.

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-   In the Milky Way, the main source of gamma rays is when high-energy particles, cosmic rays, collide with the very tenuous gas between the stars.   However, this process cannot explain the gamma rays emitted from the Sagittarius dwarf. It long ago lost its gas to the same gravity that pulled away so many of its stars.

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-  So where do the gamma rays come from?   What type of source amongst such a population produces gamma rays?  Rapidly spinning objects called "millisecond pulsars."  are the remnants of particular stars, significantly more massive than the sun, are closely orbiting another star.  

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-   Under just the right circumstances, such binary systems produce a “neutron star”, an object about as heavy as the sun but only about 20 km across, that rotates hundreds of times per second.

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-    Because of their rapid rotation and strong magnetic field, these neutron stars act as natural particle accelerators: they launch particles at extremely high energy into space.  These particles then emit gamma rays. Millisecond pulsars in the Sagittarius dwarf were the ultimate source of the mysterious cocoon.

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-   These findings shed new light on millisecond pulsars as sources of gamma rays in other old stellar systems.  The hunt for dark matter signals goes on.

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                   March 1, 2023     RADIO WAVES  -  are “light” for new telescopes        3898                                                                                                                         

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