Since the discovery in January of a mysterious radio signal from our galaxy’s center, astronomers have been baffled.
What appears in the sky, sends out radio signals at random, and then vanishes for months?
As an international team of astronomers notes in The Astrophysical Journal, the anomalous signal suggests the presence of an unidentified celestial object.
The Australian Square Kilometer Array Pathfinder (ASKAP) radio telescope in outback Western Australia was used to scan the sky when the team first discovered the signal.
Tara Murphy of the University of Sydney, one of the study’s co-authors, said the signal reappeared four more times in as many weeks.
At that point, “OK, this is real” began to dawn on us.
The ASKAP J173608.2321635 signal then vanished, only to reappear a few times a few months later.
Professor Murphy noted that the star “can come on and off in a single day, which is extremely fast for an astronomical object,” saying, “Sometimes it appears to stay on, detectable for days or weeks.”
Furthermore, the timing and signal strength are both unpredictable, with the latter becoming 100 times more intense in the radio spectrum.
What’s stranger still is that the radio waves are all aligned in the same direction as the signal rotates as it makes its way to us through the cosmos.
That eliminates nearly all of the universe’s known celestial objects, according to Professor Murphy.
However, this does not imply that we’ve found evidence of extraterrestrial life.
A mystery involving astronomy and the police
Researchers led by PhD student Ziteng Wang spent months trying to figure out the source of the anomaly after it was first discovered.
Professor Murphy described the process as “a bit like a detective story” as he tried to eliminate all the different possibilities.
They were only left with three options.
Pulsars are fast-spinning hearts of dead stars that, like an alarm clock, emit extremely fast energy pulses.
The Parkes Radio Telescope was used to search for pulsars, but no such objects were found there.
They then traveled to South Africa’s MeerKAT radio telescope, which is capable of both detecting and imaging radio signals.
There were no signals for three months before a single one that was nearly as strong as the original one faded away in February of this year.
Despite the fact that the signal exhibited some pulsar-like characteristics, there were no obvious fast pulses.
X-ray and infrared space telescopes also found no signs of a pulsar or another type of fast-spinning dead star known as a magnetar as the source of the light in the area.
The team also looked into the possibility that the signal was caused by a massive flare from a nearby star.
Professor Murphy explained that the object was so bright that it should have been visible in visible light if it was a star.
“However, we had no idea what it was because it was completely imperceptible to us.
“So now we’re in a position where the two most likely explanations have been ruled out.”
How about a “cosmic burper?”
Other than that, it could be one of the so-called “galactic center radio transients,” a ragtag group of rare objects that includes the “cosmic burper.”
We may have found one of these transients, which is exciting because there aren’t many of them, but it’s also frustrating because we have no idea what galactic center radio transients are.
It’s impossible to say for sure, but it appears that every galactic center radio transient is unique. Some emit periodic pulses of radio waves, while others do not.
While [this object’s] properties differ slightly from those already known, Professor Murphy noted that they are all unique.
This means that despite the fact that they are all grouped together, we do not have sufficient information to determine if they are connected in any way.
Professor Murphy speculated that the objects could all be unknown variable polarized objects near the galaxy’s center.
Discoveries made possible by new radio telescopes
According to Curtin University astrophysicist Gemma Anderson and the International Centre for Radio Astronomy Research, who was not involved in the study, transient objects are difficult to spot because they only turn on for a short period of time.
For weeks, months, or even years, it may not reappear through your telescope. “You want to hope your telescope is pointing at the right part of the sky when it turns on,” Dr. Anderson said.
Objects that only emit radio waves, as opposed to X-ray, optical, or infrared pulses of energy, are extremely difficult to detect.
We can now see farther into the universe than ever before thanks to radio telescopes like ASKAP Pathfinder and MeerKAT.
For this reason alone, Dr. Anderson believes that ASKAP is a particularly potent tool.
“The way we look at the universe has changed dramatically in Australia in the last few years, thanks to advances in astrophysics.”
“This new transient is just the tip of the iceberg,” says the team leader.
The ASKAP and MeerKAT telescopes are the forerunners to the Square Kilometer Array, the world’s largest radio telescope (SKA).
There may be tens of thousands of transient objects in our galaxy that have remained hidden once the SKA is operational, according to Dr. Anderson.
As for finding more of these types of objects with the ASKAP telescope, Professor Murphy expressed optimism.
“Then, once we have a large enough sample size, we will be able to determine what they are.”
In astronomy, “finding one rare thing leads to finding more like it, which leads to understanding what’s going on.”
- Milky Way: MeerKAT