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An illustration of the Nancy Grace Roman space telescope. | Photo credit: NASA
Once NASA’s Nancy Grace Roman Space Telescope launches in the next 12 to 18 months, it will be on track to exceed scientists’ initial expectations. Researchers have confirmed that Roman should be able to measure enormous seismic waves propagating across the surfaces of more than 300,000 red giant stars.
Roman is a survey telescope with a 2.4 meter mirror like the Hubble Space Telescopebut a 100 times larger field of view. Besides studying dark matter And dark energyOne of Roman’s core studies will be the Galactic Bulge Time-Domain Survey, which involves millions of people Stars in the central bulge of the Milky Way Galaxy is examined, mainly to look for it exoplanets. The idea is to use gravitational microlenses as a planet-finding device. Gravitational lensing is a technique commonly used in astrophysics to study distant objects; Because of the way spacetime distorts according to general relativity, some large objects in space (such as galaxy clusters) distort nearby traveling light, thereby magnifying, distorting, and doubling the source of that light as seen through our telescopes. Gravitational microlensing is the gravitational lensing effect on smaller scales, such as a planet.
When Roman looks at the hundreds of millions of stars in the bulge, he occasionally sees something flickering, temporarily brightening as the gravity of an unseen foreground planet amplifies its light before it moves out of alignment. However, microlensing is not the only phenomenon that can cause a star’s light to flicker. Stars are constant, twisting masses of giant convection bubbles that rise to their bubbling surfaces. Vibrations also reverberate through her interior and shake it. The frequency of these oscillations depends on a star’s temperature, structure and composition, and when the oscillations break through to the surface, they can cause a star to temporarily and subtly become brighter.
The science of studying these stellar oscillations is called asteroseismology, and the frequency of the oscillations can provide information about the masses, sizes and ages of the stars for which they are observed. A better understanding of stars, in turn, can tell astronomers about some properties of the planets that orbit them.
“With asteroseismic data, we will be able to get a lot of information about the host stars of exoplanets, and that will give us a lot of insight into exoplanets themselves,” study leader Trevor Weiss of California State University, Long Beach said in a statement opinion.
The Kepler space telescopewhich searched for exoplanets by looking for transits, was able to make asteroseismological measurements on 150,000 stars. To assess whether Roman will be able to do this, Weiss’ team applied the Kepler dataset to models of Roman’s observational abilities. In particular, they discovered that Roman will be able to detect stellar oscillations on the planet Red giant Stars that are both luminous (making them easier to detect) and have a high oscillation frequency with a period of hours to days. This fits well with Roman’s Galactic Bulge Time-Domain Survey, which will keep an eye on hundreds of millions of stars in the Milky Way’s bulge every 12 minutes over half a dozen 70.5-day periods, meaning it is tuned to the oscillations of the red giants.
“Asteroseismology with Roman is possible because we don’t have to ask the telescope to do anything it hasn’t already planned,” said Marc Pinsonneault of Ohio State University. “The strength of the Roman mission is remarkable: it is designed in part to advance exoplanet research, but we will also obtain truly rich data for other scientific areas beyond its primary focus.”
Examples of red giant sizes measured by asteroseismology. The sun is included to provide context. | Image credit: NASA/STScI/Ralf Crawford (STScI).
The bulge that houses this supermassive black hole Sagittarius A*is the oldest part of the Milky Way. Many of its stars are now aging and evolving out of the main sequence (what we call the phase of their life in which they generate energy through the main sequence). fusion from hydrogen to helium in the core).
When leaving the main sequence, the next stage in the development of a begins Sun-similar star with less than eight solar masses is to expand and become a red giant. Initial estimates of the number of red giants where Roman observed seismic waves were at 290,000, but further analysis revealed that the actual number could be much higher.
“Now that we know the survey will have a 12-minute cycle, we see that this brings our total to over 300,000 asteroseismic discoveries,” Weiss said. Depending on certain assumptions, the total number in its field of view could be as high as 648,000 red giants, including 358,000 in the bulge.
“It would be the largest asteroseismic sample ever collected,” Weiss said.
Understanding the properties of host stars will give astronomers information about the planets they find – for example, whether they are inside the planet habitable zones. The observations will also provide clues about the future of planetary systems as their star gradually begins to die, evolving into a red giant star before shedding its outer layers and leaving behind a dead man White dwarf. How quickly this happens depends on the mass of the star. More massive stars have shorter lifetimes than less massive stars. During the expansion and shedding phase, all planets that are close to the star are destroyed.
In ours Solar system‘s case, mercury, Venus and probably Earth will all be doomed to failure. However, microlensing has the advantage of being able to detect planets further away from their star, far enough away to perhaps survive the red giant stage. By discovering planets around red giants and the orbits of these planets, astronomers can better understand what fate will befall the planets in our solar system and how far away a world must be to survive. Astronomers have already noticed that a Deficit of planets orbiting red giants, and Roman’s findings will solidify our view of evolved planetary systems.
“Our work will present the statistical properties of the entire population – their typical abundance and age – so that exoplanet scientists can put the Roman measurements into context,” Pinsonneault said.
Not only will Roman’s asteroseismic discoveries teach us about planetary systems, but the ages of stars based on the asteroseismic measurements will also serve as a guide to the history of the Milky Way and, in particular, its bulge.
“We actually don’t know much about our galaxy’s bulge because it can only be seen in infrared light due to the dust in between,” Pinsonneault said. “There could be surprising populations or chemical patterns there. What if there were young stars buried there? Roman will open a completely different window into the stellar populations at the center of the Milky Way. I’m prepared for surprises.”
For example, a young stellar population could come to light if Roman measures vibrations on more massive red giants. This is because more massive stars have shorter lifetimes and therefore formed more recently.
The launch of the Roman Space Telescope is currently scheduled for fall 2026 to May 2027. Meanwhile, the new assessment of its asteroseismic capabilities has been published The Astrophysical Journal.
