As one of the most anticipated ground-based telescopes ever constructed, the Vera Rubin Observatory in Northern Chile is on the cusp of finally seeing fruition. Once its wide-field camera sees scientific first light early next year, it will begin looking for the telltale optical signatures of supernovae that lie millions or even billions of light years away.
This will help theorists better understand the true nature of both dark energy —- the unknown force that is causing the expansion of the universe to speed up —- and the effects of dark matter —- the woefully perplexing exotic matter that pervades our cosmos at every level.
Optimized to look for transient celestial phenomena, during the observatory’s estimated ten-year primary run, its Legacy Survey of Space and Time (LSST) will also identify unusual events which totally defy our current astrophysical understanding.
What Is A Transient Celestial Event?
In the strictest sense of the word, it’s something that’s new, David Buckley, the SALT Transient Phenomena principal investigator, told me at the recent ‘Cosmic Streams in the Era of Rubin’ conference in Puerto Varas, Chile. But a transient is really anything that is variable; something that has suddenly come into existence where we didn’t know of anything before, says Buckley.
Fast blue optical transients (or FBOTs) are just one example.
Fast blue optical transients are incredibly luminous events that don’t last very long at all, says Sullivan. They’ve been found in surveys, and I think they have an explosive origin, he says. A typical supernova, from the explosion of a white dwarf star, might last a few weeks and be about 10 billion times as bright as the Sun, says Sullivan. But FBOTS appear and disappear so quickly, it doesn’t give astronomers very much time to study them in detail and figure out what they are, he says.
As for what they could be?
One idea is that a supernova explosion happens inside what’s called circumstellar material, says Sullivan. This is material that is thrown off during the star’s life, but stays near the star, he says. Then when the supernova explodes, it can run into this ejected matter; heat it up, making it very hot and creating a very luminous transient event, says Sullivan.
The hope is that the LSST will find many hundreds of these FBOTs.
But the real trick to understanding what these objects are is being able to identify them in the data stream very quickly and very early on, says Sullivan.
Catching Red Dwarfs In The Act
The Rubin Observatory will also help researchers understand how stellar flares primarily from M-type stellar red dwarfs perhaps even affect the onset of life in our universe.
The median timescale of these red dwarf flare events is about 30 minutes and it’s impossible for us to predict when they’re going to happen, Riley Clarke, a graduate student in physics in astronomy at the University of Delaware in Newark, told me at the same Puerto Varas conference. That makes them a very challenging target for most astrophysical surveys, says Clarke.
The hope is that Clarke and colleagues can use the LSST to extract enough information from the image of a single flaring event to be useful for researchers studying these stars’ stellar physics.
The way we think we can do that is by using the refractive properties of our atmosphere, to infer the temperature of a stellar flare based on how much the star moves on the sky during that event, says Clarke. Their position on the sky depends on their color, he says.
Just like when you’re looking at an object at the bottom of a swimming pool and it appears distorted from its actual position, differential chromatic refraction (or DCR) is a refractive property of our atmosphere, says Clarke. The atmosphere does the same thing with starlight, so when starlight passes through our atmosphere, it’s dependent on the spectral energy distribution of the source, he says.
If more light is emitted at shorter wavelengths, then the light appears blue, says Clarke.
During its ten-year extended survey, the LSST is expected to detect some three million red dwarf flares which heat the star’s surface to an estimated 10,000 degrees Kelvin, or almost 50 percent hotter than the surface of our own Sun. It’s this sudden rise in brightness that the Rubin Observatory should detect.
Understanding the mechanics and the frequency of such flaring events goes beyond mere astrophysics. Many astrobiologists think that as the most common stars in the cosmos, red dwarfs may be prime candidates for close-in terrestrial planets that could spawn life. If a given star is too prone to such flaring, it’s not likely to be a candidate to harbor habitable planets.
Could these flares trigger life on exoplanets in orbit around such stars?
We don’t know for sure that ultraviolet energy from the flare can act as a catalyst for prebiotic life; it might just upset the chemistry enough to start enriching chemical interactions, says Riley.
