The distance from the Sun to Pluto, the farthest planet(oid), is 0.000628 light-years. The closest solar system to us, Alpha Centauri, is 4.2 light-years away. The Milky Way Galaxy is 52,850 light-years across. But Alcyoneus, the newly-discovered galaxy, is a whopping 16.3 million light-years wide.
Giant radio galaxies (GRGs, or just ‘giants’) are the Universe’s largest structures generated by individual galaxies. They were first discovered accidentally by wartime radar engineers in the 1940s, but it took over a decade to truly understand what they were — with the aid of radio astronomy. Radio astronomy is a subfield of astronomy that studies celestial objects using radio frequencies.
These giants dominate the night sky with their radio frequency signals (astronomers use different types of frequencies to study the universe). They generally consist of a host galaxy — a cluster of stars orbiting a bright galactic nucleus containing a black hole — and some colossal jets or lobes that erupt from this galactic center.
Most commonly, radio galaxies have two elongated, fairly symmetrical lobes. These radio lobes are pretty common across many galaxies — even the Milky Way has them — but for some reason, in some galaxies, the lobes grow to be immensely long. Discovering new radio galaxies could help us understand these processes — this is where the new study comes in.
Researchers led by astronomer Martijn Oei of Leiden Observatory in the Netherlands have discovered the largest single structure of galactic origin. They used the LOw Frequency ARray (LOFAR) in Europe, a network of over 20,000 radio antennas distributed across Europe.
“If there exist host galaxy characteristics that are an important cause for giant radio galaxy growth, then the hosts of the largest giant radio galaxies are likely to possess them,” the researchers explain in their preprint paper, which has been accepted for publication in Astronomy & Astrophysics.
According to the authors, this is the most detailed search ever of radio galaxy lobes, and lo and behold, the results also came in.
Alcyoneus lies some 3 billion light-years away from us, a distance that’s hard to even contemplate (though it’s not nearly the farthest object we’ve found, which lies over 13 billion light-years away). Its host galaxy appears to be a fairly normal elliptical galaxy. In fact, it almost seems too inconspicuous.
But even this could tell us something: you don’t need a particularly large galaxy or a particularly massive black hole at its center to create a radio galaxy.
“Beyond geometry, Alcyoneus and its host are suspiciously ordinary: the total low-frequency luminosity density, stellar mass and supermassive black hole mass are all lower than, though similar to, those of the medial giant radio galaxies,” the researchers write.
“Thus, very massive galaxies or central black holes are not necessary to grow large giants, and, if the observed state is representative of the source over its lifetime, neither is high radio power.”