The Birth of a Black Hole Seen for the First Time (or was it a Neutron Star?)

A black hole may have been spotted in the process of formation for the first time in history – an event astronomers have long wanted to witness. There is also a chance that the phenomenon was a neutron star – a super dense corpse of a once-massive star – being formed, which in itself would be historic.

Astronomers at the ATLAS twin telescopes in Hawaii detected a massive burst of energy on June 17th, 2017, coming from a point 200 million light years away from Earth. After a dramatic flare, the source, seen in the constellation Hercules, quickly faded. Researchers designated the object AT2018cow, although most are affectionately calling it “The Cow.”

“We knew right away that this source went from inactive to peak luminosity within just a few days. That was enough to get everybody excited because it was so unusual and, by astronomical standards, it was very close by,” said Raffaella Margutti, astrophysicist at Northwestern University.

 

The Cow
A patch of white shows the formation of a black hole or neutron star — nicknamed “The Cow” in the galaxy CGCG 137–068. Image: Sloan Digital Sky Survey.

When massive stars die, they collapse into incredibly dense objects, including neutron stars or black holes. Most normal matter, including that which makes up stars, is composed of neutrons (having no electrical charge) and positively-charged protons in the nucleus, surrounded by clouds of negatively-charged electrons. Under the enormous pull of gravity in a collapsing massive star, the electron shells surrounding atoms are crushed, and the electrons are melded with protons, forming additional neutrons. The material is so dense that a small thimbleful of a neutron star would weigh as much as Mount Everest.

The escape velocity of an object (how fast an object needs to travel to escape its surface) depends on both the mass and diameter of the object. As bodies shrink while retaining their mass, the escape velocity rises. If a stellar corpse is dense enough, it can continue to collapse until the escape velocity from its surface is greater than the speed of light. Albert Einstein determined that no object can travel through space faster than the speed of light, meaning that nothing – not even light – could escape from the gravitational grip of a black hole.

 

The closest distance material can get to a black hole and still have a chance to escape is known as the event horizon. It is possible the large burst of energy seen from The Cow was matter – perhaps from a white dwarf star – swirling around this newly-formed frontier.

Astronomers have never before witnessed the moment when a neutron star or black hole formed until now. First thought to be a supernova, this event was shown to be between 10 and 100 times more powerful than these magnificent explosions. Particles from the burst spread apart at velocities of 30,000 kilometers per hour (over 18,600 MPH), about 10 percent of the speed of light. Within 10 days, almost all the energy had dissipated.

Study of the remains of the burst showed large quantities of hydrogen and helium, suggesting it was not caused by the collision of two dense, compact objects like neutron stars.

Although we are seeing the event now, the stellar collapse occurred 200 million years ago. At that time here on Earth, all the continents were still merged together into the super-continent of Pangaea, and a massive release of methane from the oceans (perhaps aided by tremendous volcanic eruptions as Pangaea ripped apart), wiped out much of the life on Earth, opening the way for the rise of the dinosaurs.

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