Research, teaching and outreach in Physics at UW–Madison
Month: January 2024
Earth-sized planet discovered in ‘our solar backyard’
A team of astronomers have discovered a planet closer and younger than any other Earth-sized world yet identified. It’s a remarkably hot world whose proximity to our own planet and to a star like our sun mark it as a unique opportunity to study how planets evolve.
In the culmination of a decade’s worth of effort, the Dark Energy Survey collaboration of scientists analyzed an unprecedented sample of nearly 1,500 supernovae classified using machine learning. They placed the strongest constraints on the expansion of the universe ever obtained with the DES supernova survey. While consistent with the current standard cosmological model, the results do not rule out a more complex theory that the density of dark energy in the universe could have varied over time.
DES scientists presented the results January 8 at the 243rd meeting of the American Astronomical Society and have submitted them for publication to the Astrophysical Journal.
The work is the output of over 400 DES scientists, including UW–Madison physics professor Keith Bechtol and former graduate student Robert Morgan, PhD ’22.
In 1998, astrophysicists discovered that the universe is expanding at an accelerating rate, attributed to a mysterious entity called dark energy that makes up about 70% of our universe. While foreshadowed by earlier measurements, the discovery was somewhat of a surprise; at the time, astrophysicists agreed that the universe’s expansion should be slowing down because of gravity.
This revolutionary discovery, which astrophysicists achieved with observations of specific kinds of exploding stars, called type Ia (read “type one-A”) supernovae, was recognized with the Nobel Prize in Physics in 2011.
In this new study, DES scientists performed analyses with four different techniques, including the supernova technique used in 1998, to understand the nature of dark energy and to measure the expansion rate of the universe.
As a graduate student in Bechtol’s group, Morgan was part of the DES supernova working group that worked to identify type Ia supernova. This group had to address two main concerns with the data to enhance detection fidelity.
“One is that there is some leakage of other types of supernovae into the sample, so you have to calibrate the rate of misclassification,” Bechtol explains. “Also, the brightness of the supernova gives us a way of estimating its distance, but there is a distribution of how bright the Ia supernovae are. Because we are slightly less likely to detect the intrinsically fainter supernovae, there is a small bias that needs to be accounted for.”
Bechtol has been part of the DES collaboration since its formation in 2012, serving as a co-convener of the DES’s Science Release Working Group for four years and a co-convener of the Milky Way Working Group for two years. His role in this new study was in data processing and presentation.
“We collect all of the data, process it, and then release it as a coherent set of data products, both for use by the DES collaboration and as part of public releases to the community,” Bechtol says. “One of the aspects I worked on is the photometric calibration — our ability to measure the fluxes of objects accurately and precisely. It’s an important part of the supernova analysis and something that I’ve been working on continuously over the past ten years.”
Navigating new tech: Kael Hanson earns Draper Technology Innovation Fund award
Celestial navigation — charting a course through a combination of identifying star positions in the sky and knowing the time — has existed for centuries and is considerably low-res compared to modern GPS systems. So why did physics professor Kael Hanson recently receive a Draper Technology Innovation Fund (TIF) award for an invention that is based off of it?
“The pain that we’re trying to address with this technology is vulnerabilities in GPS,” Hanson says. “Everyone uses GPS, but if it drops out or gets jammed, that could be a problem, especially for the military or commercial industries like aviation or shipping that rely on it to be working and accurate 100% of the time.”
GPS is vulnerable because the satellites’ weak signals can be easily drowned out by stronger signals. Its function is susceptible to both natural (e.g. strong solar flares) and man-made (e.g. jamming or intentional signal spoofing) incidents.
Distant stars and galaxies, however, remain unaffected by whatever is happening on or near earth, so they are useful visual points of reference — unless the current conditions include daylight, clouds, or fog. Hanson’s invention, known as GRADIANT, reverts to the same concept as celestial navigation, but with a modern twist to avoid any visibility issues.
“Charged particles spinning around in the magnetic fields of our galaxy give off synchrotron radiation at radio frequencies. This technology images the sky in radio frequencies,” Hanson says. “And by doing that, basically you can see through clouds. Our technology is reliably good in all scenarios.”
Radio astronomers have been cataloging radio data for decades, and the signals remain mostly static throughout time. The invention would detect radio frequencies at the user’s location, be computationally compared to the wealth of catalogued data, and then tell the user where they are.
Hanson is not exactly sure where he came up with this idea, but he thinks it came to him when he was at the South Pole 10-15 years ago working on the Askaryan Radio Array (ARA), a radio detector installed below the ice (it is co-deployed with IceCube, which is operated by WIPAC, of which Hanson was director from 2014-2022).
“One of the background signals was the sun, and I thought ‘Oh, we can actually image the sun a couple hundred meters under the ice. Boy, wouldn’t that be interesting if you could somehow use this technology to try to figure out where you are based on where the sun is?’” Hanson says. “But then I just stuffed it away in my brain and didn’t really think about it (until recently).”
In 2021, Hanson started a company, Navigationis, to pursue his modern celestial navigation idea. This past summer, he submitted a disclosure for GRADIANT to WARF, for which a patent has now been filed. Then, he applied for and was awarded the Draper TIF funding.
Draper TIF provides a mechanism to support additional research necessary to bring new concepts and inventions to the patent and licensing stage. A main goal of the program is the eventual introduction of new products and processes into the marketplace for the public good. It is open to UW–Madison faculty and academic staff. The program is administered in partnership between Discovery to Product and the Wisconsin Alumni Research Foundation.
Hanson’s award provides $50,000, which he will use to try to make the technology more licensable.
“In order to really get this thing to the commercial state, it will take millions of dollars, it will take some additional investment,” Hanson says. “With this Draper TIF, we’re going to put together a prototype that actually proves in real hardware the working concept that’s in the patent. My hope is that I’ll have something I can point to, and venture capitalists will be that much more interested in making an investment, or the Department of Defense would be interested in supporting this work.”
Physics PhD student Stephen McKay named ALMA ambassador
Congrats to physics graduate student Stephen McKay on being named an ALMA ambassador!
ALMA, or the Atacama Large Millimeter/submillimeter Array, is the largest radio telescope in the world. It can detect light radiated by clouds of dust grains in some of the earliest and most distant galaxies in the Universe. Researchers can submit proposals to ALMA that direct data collection to observe astronomical targets at a wide range of wavelengths, in order to accomplish many cutting-edge science goals. However, ALMA receives many more proposals than there is time to operate the telescope.
That’s where McKay’s ambassadorship comes in.
“Lots of groups at UW–Madison and other places will propose to get data from these telescope arrays,” McKay says. “In February, I’ll attend a training (through the ambassador program) where they will teach me tips and tricks for writing proposals. Then in early spring, I’ll run a proposal workshop here for anyone who wants to learn how to strengthen a proposal.”
McKay is no stranger to proposing and using ALMA data. A third-year graduate student in astronomy professor Amy Barger’s research group, he expects nearly all his publications will be based on ALMA data. His research focuses on old, distant galaxies and measuring and inferring physical properties about them: How massive are they? What is their rate of star formation? What processes trigger the rapid star-formation in these systems?
“The galaxies that I mainly study are faint or hard to detect in optical wavelengths or even near-infrared wavelengths. Until about maybe 25 years ago, we didn’t know a lot of these galaxies existed because they just weren’t visible in the typical telescope images we had,” McKay says. “The portion of the observed electromagnetic spectrum where these galaxies are brightest ranges from 500 microns to nearly one millimeter, which overlaps heavily with ALMA’s spectral coverage.”
Two years ago, McKay attended an ALMA workshop to learn more about how ALMA and similar radio arrays operate. With this ALMA ambassadorship, he will now help run the workshops and offer advice on crafting stronger proposals. The ALMA Ambassador Program is run through the National Radio Astronomy Observatory’s North American ALMA Science Center (NAASC). It provides training and an up to $10,000 research grant to early-career researchers interested in expanding their ALMA/interferometry expertise and sharing that knowledge with their home institutions.
“This program is helpful for me because I will learn more in terms of how to actually do my own research, but then I can also pass along what I learn with the rest of the astronomical community,” McKay says.