Do colliding galaxies produce odd radio circles?

In the past five years, astronomers have discovered a new type of astronomical phenomenon that is vast in scale — larger than entire galaxies. They’re called ORCs (odd radio circles), and they look like giant rings of radio waves that expand outward like a shock wave. Until now, ORCs have not been observed at any wavelength other than radio, but this is a new step Paper Released on April 30, 2024, astronomers have captured X-rays associated with the ORC for the first time.

This finding provides some new clues as to what might be behind ORC formation.

While many astronomical events, such as supernova explosions, leave behind circular remnants, ORCs seem to require a different explanation.

„The power required to produce such extensive radio emission is very strong,” said Ezra Bulbul, lead author of the new paper. „Some simulations can reproduce their patterns but not their intensity. No simulation explains how ORCs form.”

ORCs can be a challenge to study because they are typically only visible at radio wavelengths. They have not previously been associated with X-ray or infrared emissions, nor have there been any signs of them at optical wavelengths. Sometimes, ORCs surround a visible galaxy, but not always (around eight known elliptical galaxies have been discovered to date).

Using ESA’s XMM-Newton telescope, Bulbul and his team observed one of the nearest known ORCs, dubbed Cloverleaf, and detected a striking X-ray component to the object.

„This is the first time anyone has seen X-ray emission associated with an ORC,” Bulbul said. „It is the missing key to unlock the secret of cloverleaf creation.”

Cloverleaf’s X-rays show gas that has been heated and excited by some process. At this point, the X-ray emissions reveal two galaxies (a total of a dozen galaxies) that have begun to merge inside the cloverleaf, heating the gas to 15 million degrees Fahrenheit.

Confused galactic connections are interesting, but they can’t explain the cloverleaf. Intergalactic mergers occur throughout the universe, while ORCs are a rare phenomenon. Something unique happens to create something like a cloverleaf.

„Connections form the backbone of structure formation, but there’s something special about this structure that rockets radio emission,” Bulbul said. „We can’t tell what it is right now, so we need more in-depth data from both radio and X-ray telescopes.”

That doesn’t mean astronomers don’t have any guesses.

„An attractive idea for the powerful radio signal is that resident supermassive black holes went through episodes of intense activity in the past, and relict electrons from that ancient activity were re-accelerated by this merger event,” said Kim Weaver, NASA project scientist for XMM. – Newton.

In other words, cloverleaf-like ORCs may require a two-part origin story — powerful emissions from active supermassive black holes, followed by galactic merger shock waves that give those emissions a second kick.

Learn more:

E. bulbul and. Al. „The origin of the Cloverleaf odd radio circular system is a constellation of constellations.” Astronomy and Astrophysics.

„X-ray satellite XMM-Newton sees 'space clover’ in new light.” NASA