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Searching the Skies

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Searching the Skies SEARCHING THE SKIES THE UNIVERSE IS FILLED WITH ONE BILLION TRILLION STARS – LOOK AT THE SKY ON A CLEAR NIGHT AND THE FEW THOUSAND THAT ARE VISIBLE ARE INCREDIBLE TO SEE. THE DR BRAD NEWTON FASCINATION OF GAZING INTO THE VASTNESS OF THE UNIVERSE HAS LED IN THE US, TO DELVE BARLOW, OF THE CULP PLANETARIUM AND HIGH POINT UNIVERSITY DEEPER INTO SPACE TO HUNT FOR A STRANGE TYPE OF STAR CALLED A HOT SUBDWARF TALK LIKE AN ASTROPHYSICIST subdwarf merges with its neighbouring white dwarf, it may explode to form a Type 1a supernova. Cosmologists use these supernovae ASTRONOMY – the study of the Universe RED GIANT – a star that has expanded to measure vast distances across the Universe to a tremendous diameter during the final and have shown that the expansion of the ASTROPHYSICS – a branch of astronomy stages of its lifetime Universe is accelerating. We frequently which studies the physical processes and observe Type 1a supernovae explosions in other properties of the Universe TYPE 1A SUPERNOVA – the explosion of galaxies, but astronomers have not caught a white dwarf upon exceeding its mass limit a binary system just before it collides and BINARY STAR SYSTEM – two stars explodes. Until now… which orbit each other VARIABLE STAR – a star whose brightness changes as we view it from Earth Brad helped discover a new binary system COSMOLOGY – a branch of astronomy containing two stars so close together that which studies the origin and evolution of the WHITE DWARF – the extremely dense, they orbit each other in under two hours. Universe Earth-sized remnant core of a dead star “Earth takes 365 days to orbit the sun,” explains Brad, “but these two stars orbit PYTHON – a scripting language used in in under two hours!” They are so close and computer coding orbiting so quickly that they are slowly spiralling in. Soon (in astrophysical terms, millions of years from now) the stars will The Universe is full of strange and wonderous star. As Dr Brad Newton Barlow, Director of interact. The white dwarf will explode as a Type things! Amongst the rarities that intrigue the Culp Planetarium and Associate Professor 1a supernova, causing one of the most powerful astrophysicists are hot subdwarfs – very hot, of Astrophysics at High Point University in the and luminous events in the Universe. dense stars. Researchers think they form US, explains, “Hot subdwarfs are definitely not from red giants stripped of their outermost a ‘normal’ type of star.” SEARCHING FOR STARS atmosphere by gravitational interactions with While few hot subdwarf stars were once another nearby star. Consistent with this STARS COLLIDING known, the European Space Agency’s Gaia theory, almost all hot subdwarfs are found in Some hot subdwarfs have a hot binary spacecraft recently discovered >30,000 new binary systems, existing in orbit with another companion such as a white dwarf. If a hot ones, giving a total of ~40,000 hot subdwarfs DR BRAD NEWTON BARLOW Director of the Culp Planetarium and Associate Professor of Astrophysics, High Point University, North Carolina, USA in our part of the Milky Way. Most interesting each time Gaia observes it.” This means FIELD OF RESEARCH of these are the variable hot subdwarfs, that without a light curve, requiring hours whose brightness varies as we observe them of telescope observations, Brad can now Stellar Astrophysics from Earth. identify potential variable stars just from the anomalously high error bars on their This variation occurs if the companion star is a brightness measurements. RESEARCH PROJECT white dwarf, which have intense gravitational Investigating hot subdwarf stars fields. This distorts the hot subdwarf from a This novel method is highly efficient, with a sphere to an ellipsoidal shape. As the binary >95% success rate. From the 40,000 known stars orbit, different sides of the ellipsoidal hot hot subdwarfs, Brad’s team have identified FUNDERS subdwarf will face Earth, causing an apparent 2000 stars that are potentially variable, and change in the observed brightness. therefore of most interest for investigation. NASA and the It would still take too long to study all these National Science Foundation This variation also occurs if the hot subdwarf individually with Earth-based telescopes has a cooler companion. As the two stars orbit, looking at small regions of the sky. Instead, the cooler companion will block, or ‘eclipse’, astrophysicists need survey-oriented systems RUNNING CODE some of the light from the hot subdwarf, with large fields-of-view to acquire follow- Once data have been downlinked to Earth, preventing it reaching Earth, so the observed up observations of numerous stars at the Brad and his team process and analyse them brightness will decrease. same time. using computer code they wrote in Python, looking for any periodic signals in the stars’ The traditional method of observing variable NASA’s TESS satellite was launched in 2018 light curves. They classify new variable stars stars involves pointing an Earth-based to search for exoplanets, but the data it by running code to examine the shape of the telescope at the star for several hours and gathers can also be useful for those who want light curve, then more codes help to determine recording a series of images. The brightness of to examine the light curves of stars. TESS important parameters such as the masses and the star in each image is plotted against time to spends 27 days pointing at a sector of the sky, radii of the stars in the binary system. produce a “light curve”, allowing variations in collecting a sequence of ~20,000 images. brightness to be quantified. Once complete, it points to a new sector WHAT NEXT FOR THE TEAM? and collects images for another 27 days. This This project is generating a lot of data for Brad With 40,000 hot subdwarfs, it would take far process will be repeated for several years, until and his team. To date they have discovered too long to study them all this way. Moreover, the entire sky has been imaged. over 100 new variable hot subdwarf stars. most of this expensive telescope time would be Some of these are hot subdwarfs in orbits with wasted, as most hot subdwarfs are not variable. LIMITED BANDWIDTH red dwarfs and white dwarfs, which will help Brad, along with his students and collaborators, Even though TESS is imaging all the stars it astrophysicists understand how hot stars evolve devised a new method to ascertain which stars sees, many of these observations are ‘wasted’ in binary systems. Other systems turned out they should focus investigations on. because there simply is not enough bandwidth not to be hot subdwarf binaries at all, but available to downlink all the data back to Earth. strange “cataclysmic variables”, in which mass THE GAIA ERROR BAR METHOD is transferring from a red dwarf to a white Brad and the team realised that when the Astronomers who want to access these dwarf. Many of the new variables have yet to Gaia spacecraft records a star’s brightness, observations must compete against each be classified. the associated error can indicate whether other, making a case for why the data they the star is variable. “Take two stars with the are interested in deserves to be sent to Earth. The team will identify which of these systems same brightness – one that is constant in Brad’s team is fortunate to have had two cases are most interesting for further research. time, another that changes in brightness,” accepted. These are providing them with 10 They will apply to visit Earth-based telescopes, explains Brad. “The scatter in Gaia’s brightness million individual brightness measurements where they will conduct important follow-up measurements will be larger for the variable from TESS, allowing them to generate light observations enabling them to analyse these star, because it has a different brightness curves for several thousand hot subdwarf stars. incredible new stars. ABOUT ASTROPHYSICS To study the physics of the Universe, an inability to control the experiment, or to even discover something new, they must not tell astrophysicist spends a lot of time writing and see what we are studying, forces us to be very anyone else about it, including Brad, for 15 debugging computer code to run simulations careful when interpreting our results.” minutes. Why? “For those 15 minutes, they are or analyse data. “On some days this goes the only being in the entire Universe to know smoothly,” says Brad. “But I’ve spent entire “It’s fun to uncover the secrets of the that bit of information,” explains Brad. days banging my head against my keyboard, Universe!” says Brad. “I enjoy the thrill that trying to find one small error in my code!” comes with making new discoveries. It makes me feel like I’m a part of something bigger than While a physicist, biologist or chemist can myself.” PATHWAY FROM go into their laboratory and control their experiment, astronomers do not have such For Brad, one of the most rewarding aspects SCHOOL TO luxuries. “The Universe provides us a one- is watching his students develop into scientists ASTROPHYSICIST way information stream in the form of light and make discoveries of their own. He has a and gravitational waves,” explains Brad. “The rule for everyone who works with him: if they At school, take maths, physics and computing courses, and Brad recommends gaining experience in coding. In college/university, your courses will focus on astronomy, physics, maths and computer science. Brad advises, “No matter what stage you’re at, reach out to faculty members or astronomers to see if you can participate in the research they do.” HOW DID BRAD BECOME Many astrophysicists will have a degree in astronomy, astrophysics or space science, AN ASTROPHYSICIST? but a broader degree in physics, maths or geophysics can also lead to a career in astrophysics.
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