Signs of supermassive black holes merging spotted: Astronomers
LONDON : Astronomers have found evidence for a large number of double supermassive black holes, the likely precursors of gig antic black hole merging events.
This confir ms the current understanding of cosmological evolution — that galaxies and their associated black holes merge over time, forming bigger and bigger galaxies and black holes, said an international team of scientists led by astronomers from the University of Hertfordshire, UK.
For the research, published in the journal Monthly Notices of the Royal Astronomical Society, the team looked at radio maps of powerful jet sources and found signs that would usually be present when looking at black holes that are closely orbiting each other.
Super massive black holes emit powerful jets. When super massive binary black holes orbit, it causes the jet emanating from the nucleus of a galaxy to periodically change its direction.
Astronomers studied the direction that these jets are emitted in, and variances in these directions; they compared the direction of the jets with the one of the radio lobes (that store all the particles that ever went through the jet channels) to demonstrate that this method can be used to indicate the presence of supermassive binary black holes.
“We have studied the jets in different conditions for a long time with computer simulations. In this first systematic comparison to high-resolution radio maps of the most powerful radio sources, we were astonished to find signatures that were compatible with jet precession in three quarters of the sources,” said lead author Martin Krause, lecturer at the varsity.
The fact that the most powerful jets are associated with binary black holes could have important consequences for the formation of stars in galaxies; stars form from cold gas, jets heat this gas and thus suppress the formation of stars.
A jet that always heads in the same direction only heats a limited amount of gas in its vicinity. However, jets from binary black holes change direction continuously.
T herefore, they can heat much more gas, suppressing the formation of stars much more efficiently, and thus contributing towards keeping the number of stars in galaxies within the observed limits, the astronomers explained. NEW YORK: More than 400 million years ago, ancient oceans were teeming with many fish that might seem alien in today’s seas.
Back then some wore plates of bony armor and lacked jaws, such as the arandaspids, which looked like a clam with a tail. The heterostracans sometimes resembled underwater armadillos with spikes. There were also galeaspids, some of which sported swordlike helmets, and the osteostracans, which had horseshoeshaped heads.
Not all jawless fish were heavily armored. The thelodonts, for example, had torpedo-shaped bodies and bony scales that looked like shark skin. Some anaspids had scales and a leaf-shaped body. And then came the first jawed fishes such as armored placoderms, some of which used their tanklike exterior and razorsharp teeth to dominate the water world.
Scientists have long wondered where in the sea these extinct fish groups and their living relatives first evolved. Was it the open ocean? Perhaps on coral reefs? Or maybe in the depths of the abyss?
Figuring out the answer has been difficult. While there is an abundance of fish fossils from about 420 million years ago, the ancient fossil record gets scarce farther back at about 480 million years ago, when fish are believed to have first appeared.
Now, a new study suggests that fish first swam in the shallows around the coasts of supercontinents before they diversified and conquered the world’s waters. The findings, which were published Thursday in the journal Science, also provide insight into the origins of the vertebrates that became the forebears of our ancestors who first ventured onto land.
To better understand the ancient evolutionary history of fish, the researchers trawled through the scientific literature and created a database with more than 2,700 fossil records of jawed and jawless fish from every continent that stretched from 480 million to 360 million years ago. The database allowed the team to determine where in the ocean the ancient fish groups lived and evolved.