- 3590 - JAMES WEBB - and Event Horizon telescopes. James Webb Space Telescope is now experiencing all seasons – from hot to cold – as it undergoes the thermal stability test, May, 2022. To complete the telescope’s commissioning, astronomers will measure the detailed performance of the science instruments before they start routine science operations in the summer.
--------------------- 3590 - JAMES WEBB - and Event Horizon telescopes
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- James Webb Space Telescope is now experiencing all seasons – from hot to cold – as it undergoes the thermal stability test, May, 2022. To complete the telescope’s commissioning, astronomers will measure the detailed performance of the science instruments before they start routine science operations in the summer.
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- With the telescope aligned and the observatory near its final cryogenic temperature, astronomers are ready to begin the last group of activities;
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---------------- The instruments, the Near-Infrared Camera (NIRCam),
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---------------- Near-Infrared Spectrometer (NIRSpec),
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--------------- Near-Infrared Imager and Slitless Spectrometer (NIRISS),
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---------------- Mid-Infrared Instrument (MIRI),
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- The Fine Guidance Sensor (FGS) have been powered up and safely cooled. They have operated their mechanisms and detectors, including filter wheels, grating wheels, and the NIRSpec microshutter assembly.
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- The Webb optics team used images of isolated stars taken with each of the instruments to align the primary and secondary mirrors.
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- They will begin an extensive suite of calibrations and characterizations of the instruments using a rich variety of astronomical sources. They will measure the instruments’ throughput, that is, how much of the light that enters the telescope reaches the detectors and is recorded.
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- There is always some loss with each reflection by the mirrors of the telescope and within each instrument, and no detector records every photon that arrives. They will measure this throughput at multiple wavelengths of light by observing standard stars whose light emission is known from data obtained with other observatories combined with theoretical calculations.
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- The “astrometric calibration” of each instrument maps the pixels on the detectors to the precise locations on the sky, to correct the small but unavoidable optical distortions that are present in every optical system.
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- They do this by observing the Webb astrometric field, a small patch of sky in a nearby galaxy, the Large Magellanic Cloud. This field was observed by the Hubble Space Telescope to establish the coordinates of about 200,000 stars to an accuracy of 1 milli-arcsec (less than 0.3 millionths of a degree).
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- Calibrating this distortion is required to precisely place the science targets on the instruments’ field of view. To get the spectra of a hundred galaxies simultaneously using the “NIRSpec microshutter assembly“, the telescope must be pointed so that each galaxy is in the proper shutter, and there are a quarter of a million shutters!
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- They measure the sharpness of the stellar images, that astronomers call the ‘point spread function.’ They already know the telescope is delivering to the instruments image quality that exceeds prelaunch expectations, but each instrument has additional optics.
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- These optics perform a function, such as passing the light through filters to get color information about the astronomical target or using a diffraction grating to spread the incoming light into its constituent colors. Measuring the point spread function within each instrument at different wavelengths provides an important calibration for interpreting the data.
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- For some observations, it is sufficient to point the telescope using the position of a guide star in the “Fine Guidance Sensor” and know the location of the science target relative to that guide star. This places the science target to an accuracy of a few tenths of an arcsecond.
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- However, in some cases more precision is necessary, approximately a hundredth of an arcsecond. For coronagraphy, the star has to be placed behind a mask so its light is blocked, allowing the nearby exoplanet to shine through.
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- In time series observations, they measure how an exoplanet’s atmosphere absorbs the stellar light during the hours it takes to pass in front of its star, allowing us to measure the properties and constituents of the planet’s atmosphere. Both of these applications require that the instrument send corrections to the telescope pointing control system to put the science target precisely in the correct location within the instrument’s field of view.
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- Most astronomical objects are so far away that they appear to be stationary on the sky. However, this is not true of the planets, satellites and rings, asteroids, and comets within our own solar system. Observing these requires that the observatory change its pointing direction relative to the background guide stars during the observation.
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- When the commissioning is complete by July, 2022, JAMES is fully ready for its scientific mission.
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- There is another new telescope, the “Event Horizon Telescope” that is collecting data to create new images of the Milky Way's supermassive blackhole. A legion of other telescopes including three NASA X-ray observatories in space was also watching.
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- Astronomers are using these observations to learn more about how the black hole in the center of the Milky Way galaxy, Sagittarius A * (Sgr A* for short), interacts with, and feeds off, its environment some 27,000 light years from Earth. You are just this far away fro a blackhole.
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- When the Event Horizon Telescope (EHT) observed Sgr A* to make the new image, scientists in the collaboration also peered at the same black hole with facilities that detect different wavelengths of light.
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- With this multiwavelength observing campaign astronomers assembled X-ray data from:
---------------- NASA's Chandra X-ray Observatory,
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---------------- Nuclear Spectroscopic Telescope Array (NuSTAR),
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---------------- Neil Gehrels Swift Observatory;
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--------------- radio data from the East Asian Very Long-Baseline Interferometer (VLBI) network
--------------- radio data from the Global 3-millimeter VLBI array;
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--------------- infrared data from the European Southern Observatory's Very Large Telescope in Chile.
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- The Event Horizon Telescope has captured yet another remarkable image, this time of the giant black hole at the center of our own home galaxy. One important goal was to catch X-ray flares, which are thought to be driven by magnetic processes similar to those seen on the Sun, but can be tens of millions of times more powerful.
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- These flares occur approximately daily within the area of sky observed by the EHT, a region slightly larger than the event horizon of Sgr A*, the point of no return for matter falling inward.
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- Another goal was to gain a critical glimpse of what is happening on larger scales. While the EHT result shows striking similarities between Sgr A* and the previous black hole it imaged, M87*, the wider picture is much more complex.
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- If the new EHT image shows us the eye of a black hole hurricane, then these multiwavelength observations reveal winds and rain the equivalent of hundreds or even thousands of miles beyond.
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- One of the biggest ongoing questions surrounding black holes is exactly how they collect, ingest, or even expel material orbiting them at near light speed, 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.
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- “Chandra” images of hot gas around Sgr A* are crucial for accretion studies because they tell us how much material is captured from nearby stars by the black hole's gravity, as well as how much manages to make its way close to the event horizon.
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- Astronomers can largely agree on the basics that black holes have material swirling around them and some of it falls across the event horizon forever. The comparison of the models with the measurements gives hints that the magnetic field around the black hole is strong and that the angle between the line of sight to the black hole and its spin-axis is low, less than about 30 degrees.
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- If this is confirmed this means that from our vantage point we are looking down on Sgr A* and its ring more than we are from side-on, surprisingly similar to EHT's first target M87*.
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- The researchers managed to catch X-ray flares from Sgr A* during the EHT observations: a faint one seen with Chandra and Swift, and a moderately bright one seen with Chandra and NuSTAR. X-ray flares with a similar brightness to the latter are regularly observed with Chandra, but this is the first time that the EHT simultaneously observed Sgr A*, offering an extraordinary opportunity to identify the responsible mechanism using actual images.
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- The millimeter-wave intensity and variability observed with EHT increases in the few hours immediately after the brighter X-ray flare, a phenomenon not seen in millimeter observations a few days earlier.
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- These are not ordinary telescopes. Galileo would be proud.
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May 30, 2022 JAMES WEBB - and Event Horizon telescopes 3590
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--------------------- --- Tuesday, May 31, 2022 ---------------------------
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