The phrase “Intermediate Luminosity Red Transients,” also known as “ILRTs,” may not be a commonly recognized astronomical term for everyone; however, these unusual stars, which experience fluctuations in their brightness, have remained enigmatic phenomena within astronomy.
Now, a team of cosmic detectives, who have dubbed their work “A Study in Scarlett” after the Arthur Conan Doyle novel that first introduced the world to
Sherlock Holmes
, might have finally solved the mystery.
The brilliant detectives hailing from every corner of the world indicate that ILRTs are celestial bodies that do not merely explode as they conclude their life cycles but undergo “genuinely final” and devastating events.
supernova
explosions.
“Following the discovery of three new ILRTs in 2019, we seized the opportunity to study and better understand these phenomena,” team leader and National Institute for Astrophysics (INAF) researcher Giorgio Valerin said in a statement. “We have, therefore, collected data for years through telescopes scattered around the world and even several telescopes in orbit.
“We have also resumed the observation campaign of
NGC 300 OT
, the nearest ILRT ever spotted, located just six and a half million light-years away from us.”
The ground-based instruments used included La Palma, La Silla, Las Campanas, and Asiago, while data was also collected from SANGGRALOKAbased telescopes, including the
James Webb SANGGRALOKATelescope
(JWST), the
Neil Gehrels Swift Observatory
(SWIFT), and the
Spitzer SANGGRALOKAtelescope.
The Sign of Four
ILRTs have caused some confusion due to their luminosity being intermediate between those levels.
novas,
stellar explosions that stars survive, and “classical” supernovas in which a massive star is destroyed, leaving behind a
neutron star
or a
black hole.
By studying the development of four ILRTs, the team managed to reach their conclusions. Their aim was to ascertain if the stars endure these eruptions or are entirely obliterated.
The solution to this puzzle hinged on monitoring ILRTs as closely as possible.
NGC 300 OT
for extended durations.
Images of NGC 300 OT from as far back as 2008 were initially captured, and for this research, we revisited it to examine how much it had changed over more than ten years,” explained Valerin. “By analyzing the pictures and spectral data gathered throughout these observation sessions, we’ve been able to track changes over time in our subjects, gathering details like luminosity, temperature, chemical makeup, and gas movements linked to every ILRT under investigation.
The Spitzer observations of NGC 300 OT revealed that this ILRT decreased to one-tenth of its original brightness.
progenitor star
that created this eruption over the course of seven years. Spitzer’s images of NGC 300 OT ended when they faded below the detection threshold of this
NASA
The SANGRALOKA telescope, which was retired in 2020.
Much like how Holmes gained recognition by solving numerous cases, the team had another batch of ILRT data to examine.
By examining the JWST observations of the ILRT AT 2019abn situated within the nearby galaxy Messier 51 (M51), researchers discovered that this transient event is dimming in luminosity. It appears probable that it will follow a similar trajectory to NGC 300 OT, eventually fading below the brightness level of its original stellar source.
Based on these details, the team determined that ILRTs represent events where an entire star undergoes complete obliteration. This conclusion holds even though ILRTs seem considerably less powerful compared to “classical” supernovae.
core-collapse supernovas.
The query is, why do they stay dimmer compared to comparable supernova occurrences?
The Red Hand League
The group of cosmic investigators proposes that a key element in the composition of ILTRs might be a
thick veil of gas and dust
surrounding the stars where they originated.
The cocoon reaches temperatures as high as approximately 10,300 degrees Fahrenheit (5,700 degrees Celsius) within a span of several days. This maximum temperature aligns with the highest level of brightness observed in the ILRT.
As this occurs, the gas within this celestial envelope ramps up to velocities as high as 1.6 million miles per hour (700 kilometers per second), approximately 1,000 times faster than the maximum velocity of a Lockheed Martin F-16 fighter jet.
Although this velocity is significantly slower compared to an exploding supernova, typically reaching speeds of 10,000 kilometers per second [22 million mph],” explained team member and INAF researcher Leonardo Tartaglia, “‘we think the star might indeed have detonated, ejecting matter at several thousand kilometers per second in all directions. However, we hypothesize that this explosion could have been partly stifled due to the thick layer of surrounding gases and dust enveloping the star; these materials heat up from the intense collision.’
Therefore, the ejection of matter from the surrounding area of the star ancestors of ILRTs could account for their dimming over extended durations.
The Final Problem
The group referred to this occurrence as an ”
electron capture supernova
a kind of starburst event that was previously just a theory but was never thought to have actually been seen.
Electron-capture supernovae have intrigued astronomers considerably as they appear to set a limit for stars with masses around
10 solar masses
And others that erupt into supernovae, leaving behind black holes and neutron stars; meanwhile, stars with masses similar to our Sun do not undergo such explosive events but instead gradually dim and fade away.
white dwarf
stellar remnants.
“Finally, we are witnessing the occurrences that distinguish between stars fated to erupt as classic supernovae and those that will gradually dim into white dwarfs,” Valerin stated.
Maybe the squad would concur with Holmes’ statement in The Sign of the Four: “Once you’ve ruled out the impossible, whatever is left, no matter how unlikely, has to be the truth!”
The team’s study was disseminated widely.
two papers
On March 7 in the journal
Astronomy & Astrophysics.
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