July 17, 2022
Sunday, July 17, 2022
Wow! What a difference a 6.5-meter telescope has over 2.4-meter telescope. The beauty and exquisite details we can see with the James Webb Space Telescope compared to the Hubble Space Telescope in the infrared is astounding. Intellectually, we knew, of course, what the difference would be but the first images and data released last Monday/Tuesday made it clear at the heart or gut level.
The objects chosen (a very distant galaxy cluster, a planetary nebula ejected from a dying star, the spectra of the atmosphere of an exoplanet, a group of interacting galaxies, and the protostars and dust pillars in a star formation nebula) were selected because of their beauty, they represent the most scientifically interesting type of objects, they highlight the capabilities of Webb, and they represent the four main science areas of Webb: the first stars and galaxies of the early universe, how galaxies assemble over time, star and planet formation, and exoplanets and objects in our solar system. Explore the images at www.nasa.gov/webbfirstimages .
The week before, the LZ dark matter team released a report on their efforts to detect dark matter particles. Finding out what is dark matter is one of the greatest puzzles of physics and developing the experiment that would definitively tell us what it is would be worth a Nobel Prize (or two). Dark matter is a type of matter that has mass, responding to gravity, but it does not interact with electromagnetic radiation—the various forms of light (e.g., visible light, x-rays, infrared, radio, etc.), so it does not block or scatter light like ordinary matter does. Since dark matter doesn't interact with electromagnetic radiation, it can pass through ordinary matter. On astronomical scales we know it's there because of its gravitational effect—making objects we can see (stars, galaxies, gas clouds, etc.) move a lot faster than we'd expect from the gravity of just those objects. The gravity of dark matter bends or warps the spacetime around it as described by Einstein's Theory of General Relativity, so even though the dark matter does not interact with light, it does bend the path of the light by bending the spacetime the light travels through. We've used the bending of light to map out the location and amount of the dark matter in galaxy clusters.
Detecting dark matter would improve our understanding of the quantum realm as well as the formation of large-scale structures of galaxies, galaxy clusters, and superclusters. While the techniques and technology developed to detect the dark matter will have spinoffs of more practical or commercial use, it's the natural human curiosity and desire to more fully understand physical reality that drives the research.
Dark matter detectors are built far below the surface to shield them from cosmic rays from space just like the detectors we use for the other ghost particles of the atomic realm, neutrinos. Neutrinos have a tiny mass but the dark matter particles are expected to be many tens of thousands of times more massive. Both neutrino and dark matter detectors look for tell-tale flashes of light and ricocheting nuclei that have been hit by the ghost particles. These events are extremely rare. We've been measuring neutrinos since the 1970s but have yet to definitively detect dark matter particles.
The biggest dark matter detector built so far is the “LUX-ZEPLIN” or “LZ” for short, located 4850 feet below ground at the Sanford Underground Research Facility in Lead, South Dakota. The all-caps in the name means it's an acronym of obscure physics terms strung together by a group of physicists who are also fans of rock music. LZ uses 7 metric tons of liquid Xenon in a large tank as its detection medium. Two other dark matter detectors in China and Italy are slightly smaller but similar design: the PandaX-4T in China uses 3.7-tons of Xenon and the XENONnT in Italy uses 5.9 tons of Xenon. The LZ team released a status report after 65 days worth of data collection of a 3 to 5-year experiment showing the detector is functioning correctly but no dark matter has been conclusively detected yet.
In our night sky, some flashes of light we'll have a much easier time seeing are the Delta Aquariid meteors in the meteor shower that runs between mid-July to mid-August with a peak on the night of July 29/30. The Delta Aquariids can produce up to 35 meteors per hour for those in the southern tropics. For Kern County on a dark sky, 12-15 meteors per hour is more likely what we can see. This year, the moon will be just one day past new phase, so there will no moon to wash out the fainter meteors as they streak across the sky at 25 miles per second.
Tomorrow night the moon will slide past Jupiter. The moon will be at last quarter on the night of July 19/20 and on the early morning of July 21, it will be right next to Mars—less than 3 degrees apart. On the early morning of July 26, a thin waning crescent will be next to brilliant Venus.
When temperatures get above 105 deg F, senior citizens and others at risk from extreme heat can find relief at a cooling center. I hope you'll be able to go out and enjoy a truly dark sky filled with stars sometime this summer!
—
Nick Strobel
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com
