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Illustration of the Roman Space Telescope by Nancy Grace. | Credit: NASA
Once NASA's Nancy Grace Rome Space Telescope launches in the next 12 to 18 months, it will exceed scientists' initial expectations. Researchers have confirmed that Roman will be able to measure the enormous seismic waves rippling across the surface of more than 300,000 red giant stars.
Novel is a survey telescope with an 8-foot (2.4 meter) long mirror similar to a telescope Hubble Space Telescopebut the field of view is 100 times larger. Besides studying dark matter And dark energyone of Roman's main studies will be the exploration of the Galactic bulge in the time domain, in which millions stars in the central convexity Milky Way Galaxy will be studied mainly to find exoplanets. The idea is to use gravitational microlensing as a planet-finding device. Gravitational lensing it is a technique often used in astrophysics to study distant objects; Because of the way spacetime is distorted according to general relativity, some huge objects in space (such as clusters of galaxies) distort light passing nearby, thereby magnifying, distorting, and duplicating the source of that light as seen through our telescopes. Gravitational microlensing refers to gravitational lensing on smaller scales, such as on a planet.
Looking at the hundreds of millions of stars in the bulge, Roman occasionally notices some flickering, temporarily becoming brighter as the gravity of an unseen planet in the foreground amplifies their light before moving away. However, microlensing is not the only phenomenon that can cause a star's light to flicker. Stars are constant writhing masses of huge convective bubbles rising to their seething surface. The vibrations also reverberate through their insides, shaking them. The frequency of these oscillations depends on the temperature, structure and composition of the star, and when the oscillations break through to the surface, they can cause a temporary, minor brightening of the star.
The science that studies these stellar wobbles is called asteroseismology, and the frequency of the wobbles can reveal the masses, sizes and ages of the stars that experience them. In turn, a better understanding of stars can give astronomers information about some of the properties of the planets orbiting them.
“With asteroseismic data, we will be able to get a lot of information about the host stars of exoplanets, and this will give us a lot of information about the exoplanets themselves,” said study leader Trevor Weiss of California State University, Long Beach. statement.
Kepler Space Telescopewho hunted for exoplanets by observing transits, was able to take asteroseismological measurements of 150,000 stars. In assessing whether Roman could do the same, Weiss' team applied Kepler's data set to models of Roman's observational abilities. In particular, they discovered that Roman would be able to detect stellar fluctuations at red giant stars that are both luminous (making them easier to detect) and have a high frequency of oscillations with periods ranging from hours to days. This fits well with Roman's time-domain study of the Galactic Bulge, which will closely monitor hundreds of millions of stars in the Milky Way galaxy's bulge every 12 minutes for half a dozen 70.5-day stretches, meaning it will be tuned to the vibrations of red giants.
“Asteroseismology with Roman is possible because we don't have to ask the telescope to do something it hasn't already planned,” said Mark Pinsonneault of Ohio State University. “The power of the Rome mission is amazing: it's partly designed to advance exoplanet science, but we'll also get really rich data for other scientific fields outside of its core focus.”
Examples of red giant sizes measured using asteroseismology. The sun is included to provide context. | Credit: NASA/STScI/Ralph Crawford (STScI).
The bulge that contains supermassive black hole Sagittarius A*is the oldest part of the Milky Way galaxy. Many of its stars are now aging, evolving off the main sequence (this is what we call the stage of their lives when they generate energy through merger hydrogen to helium in the core).
Leaving the main sequence, the next stage of evolution Sun-like star with number less than eight solar masses is to expand and become a red giant. Initial estimates of the number of red giants from which Roman could observe seismic waves were 290,000, but deeper analysis suggested that the actual number could be much higher.
“Now that we know the survey will be done at 12-minute intervals, we find that this increases our numbers to more than 300,000 asteroseismic detections,” Weiss said. Depending on certain assumptions, the total number could be as high as 648,000 red giants in view, of which 358,000 are in the bulge.
“This will be the largest asteroseismic sample ever collected,” Weiss said.
Understanding the properties of their parent stars will give astronomers information about the planets they find—for example, whether they are in habitable zones. The observations will also provide clues to the future of planetary systems as their stars begin to gradually die, turning into a red giant star before shedding their outer layers and leaving behind a dead star. white dwarf. How quickly this happens depends on the mass of the star. More massive stars have shorter lives than less massive stars. During the expansion and ejection phase, any planets orbiting the star are destroyed.
In our solar systemcase, Mercury, Venus and probably Earth everyone will be doomed. However, microlensing has the advantage of being able to detect planets that are farther away from their star, far enough away to possibly survive the red giant stage. By discovering planets around red giants and the orbits of those planets, it will help astronomers better understand what fate befalls the planets in our solar system and how far away a world must be to survive. Astronomers have already noticed planet shortage orbit red giants, and Roman's discoveries will strengthen our picture of evolved planetary systems.
“Our work will lay out the statistical characteristics of the entire population—what their typical size is and their age—so that exoplanet scientists can put the Roman measurements into context,” Pinsonneault said.
Not only will Roman's asteroseismic discoveries tell us about planetary systems, but the ages of stars based on asteroseismic readings will serve as a guide to the history of the Milky Way and, in particular, its bulge.
“We actually don't know much about the bulge of our galaxy because, due to all the interstitial dust, it can only be seen in infrared light,” Pinsonneault said. “There could be amazing populations or chemical structures there. What if young stars are buried there? The novel will open a completely different window into the stellar population at the center of the Milky Way. I'm ready to be surprised.”
For example, a young population of stars could be revealed if Roman measures wobbles on more massive red giants. This is because more massive stars live shorter lives and therefore formed later.
The Rome Space Telescope is currently scheduled to launch in the fall of 2026 and May 2027. Meanwhile, a new assessment of its asteroseismic capabilities was published in the journal Astrophysical Journal.
