Tag Archives: cygnus

Massive Black Hole Could Challenge Stellar Evolution Theories

Astronomers have used the Very Long Baseline Array (VLBA) to discover that the first black hole ever detected is actually much larger than previously believed. So large, at 21 times the mass of the Sun, that it challenges existing theories about the evolution of stars and how they form black holes. These constraints should limit stellar black holes in binary systems to about 15 solar masses.

Cygnus X-1 is a Milky Way binary system that contains a black hole and a supergiant companion star feeding it gas and other material. First discovered in 1964, the binary system has gone on to become one of the most intensely studied objects in astronomy. Yet, our familiarity with Cygnus X-1 doesn’t mean it can’t still deliver a surprise or two.

An artist’s impression of the Cygnus X-1 system. A stellar-mass black hole orbits with a
companion star located 7,200 light-years from Earth. (ICRAR)

In addition to finding the black hole is 50% more massive than prior estimates, near 21 solar masses as opposed to 15 solar masses, the team also discovered that the companion star also has a greater mass than previous measurements had revealed. The system as a whole is 20% further away than previously calculated–7,200 light-years from Earth as opposed to 6,100 light-years.

“We know that Cygnus X-1 hosts a black hole that is 21 times the mass of the Sun. We also learned that the supergiant companion star in Cygnus X-1 is also more massive than we had thought, with a mass of about 40 times the mass of the Sun,” Professor James Miller-Jones, the International Centre for Radio Astronomy Research (ICRAR), Curtin University, Australia, tells ZME Science. “The revised masses and distances also lead to an updated orbital separation between the star and the black hole — they orbit each other at a separation of one-quarter the distance from the Earth to the Sun.”

Cygnus X-1: New findings show the binary system is more massive and further away than previous estimates implied. (ICRAR)

The finding, published in the latest edition of the journal Science, means that Cygnus X-1 contains the largest black hole created through the collapse of a star alone, that has ever been detected with traditional electromagnetic astronomy without the use of gravitational waves. Larger black holes do of course exist, but these are formed through other mechanisms such as mergers between smaller black holes after that initial stellar collapse.

Miller-Jones, the study’s lead researcher, goes on to explain that the team also learned that the black hole is spinning very rapidly , close to its maximum possible speed. 

“With all this new information, we were able to propose a likely scenario for how this system formed, which can explain its observed properties.”

Professor James Miller-Jones, ICRAR, Curtin University

The finding doesn’t conform to current theories about black hole formation and stellar development in binary systems as its mass is greater than the limit imposed on such an object. 

How Cygnus X-1 Challenges Theories of Stellar Evolution

The team chanced on their finding whilst conducting an ambitious project to observe Cygnus X-1 almost continuously over a full 5.6-day orbit with the network of radio telescopes that comprise VLBA and X-ray telescopes. The aim of the research was to better understand how gas being fed into a black hole from a binary partner via a spiraling accretion disc connects to powerful jets of material that launch out from near the central region at near light speed.

“We had not originally aimed to refine the distance and the mass of the black hole but realised that our data would allow us to do so, by accounting properly for the effects of the black hole orbit.  But there is still a wealth of data from this rich observing campaign that we are looking to analyse more fully.”

Professor James Miller-Jones, ICRAR, Curtin University

“Black holes form from the deaths of the most massive stars when they run out of fuel and gravity takes over,” says Miller-Jones. “The mass of the resulting black hole is set by the initial mass of the star from which it formed — which we call the progenitor star — the amount of mass that star lost in winds over its lifetime, and any interactions with a nearby companion star.” 

Miller-Jones continues, saying massive stars launch very powerful winds from their surfaces, which leads to significant mass loss over their few-million year lifetimes. Some of the later phases of star’s evolution have particularly strong winds — determined by the abundance of elements heavier than helium in the gas from which the star was formed. More heavy elements mean stronger winds, and ultimately, a less massive star immediately before gravitational collapse. 

While some stars can also lose further mass in supernova explosions as they collapse to form a black hole, the evidence suggests that in Cygnus X-1, there was no explosion, and the star collapsed directly into a black hole,” says Miller-Jones. “The stronger the stellar winds during the late evolutionary phases of the star, the less massive we would have expected the black hole to be.”

An artist’s impression of the Cygnus X-1 system. This system contains the most massive stellar-mass black hole ever detected without the use of gravitational waves, weighing in at 21 times the mass of the Sun. (ICRAR)

At first, the team wasn’t totally aware of just how significant their discovery of mass disparities in the Cygnus X-1 binary system was. “I think that our biggest surprise was when we appreciated the full implications of our measurements,” Miller-Jones says. “As observational astronomers, my team and I had already found that we could revise the source distance and the black hole mass. However, it was not until I visited a colleague, Professor Ilya Mandel of Monash University, who is a theoretical astronomer, that we realised how important this actually was.”

Mandel–co-author on the resulting paper– realised that a 21-solar mass black hole was too massive to form in the Milky Way with the constraints in place due to the current prevailing estimates of the amount of mass lost by massive stars in stellar winds.

“The existence of such a massive black hole in our own Milky Way galaxy has shown us that the most massive stars blow less mass off their surface in winds than we had previously estimated. This improves our knowledge of how black holes form from the most massive stars.”

Professor James Miller-Jones, ICRAR, Curtin University

Cygnus X-1: No Stranger to Contraversy

The team’s findings have allowed them to put forward a scenario that would allow the formation of a 21 solar mass black hole in a binary system. “We suggest that the star that eventually collapsed into a black hole began its life a few million years ago with a mass of 55-75 times the mass of the Sun,” Miller-Jones tells ZME.  “Over its lifetime, it was close enough to its companion–the current supergiant–that gas from its surface was transferred onto its companion.  This removed the outer layers of the black hole progenitor and caused it to rotate more rapidly because the two stars were always keeping the same face towards one another. 

“Eventually, possibly as recently as a few tens of thousands of years ago the progenitor star collapsed directly into a black hole–of close to its current mass of 21 times the mass of the Sun–without a supernova explosion.”

Professor James Miller-Jones, ICRAR, Curtin University



Additionally, as well as gaining an insight into the black hole’s birth, Miller-Jones believes the team’s results could also indicate how the system could end its life. “Finally, we considered the eventual fate of this system,” the paper’s lead author says. “While the current companion star may eventually form a black hole, the separation of the two stars is such that the two black holes are unlikely to merge on a timescale comparable to the age of the Universe.”   

A companion paper appearing at the same time in the Astrophysical Journal will delve deeper into these elements of the research.

A closer look at the massive star in the Cygnus X-1 binary (ICRAR)

This isn’t the first time that Cygnus X-1, and more specifically its black hole, has sparked discussion in the fields of astronomy and cosmology. As speculation grew during that the intense X-ray source in the region was the result of a black hole, renowned physicist Stephen Hawking bet fellow scientist Kip Thorne–well known for his black hole work–in 1974 that Cygnus X-1 did not contain a black hole.

“This was a form of insurance policy for me. I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine Private Eye. If black holes do exist, Kip will get one year of Penthouse.”

Stephen Hawking, A Brief History of Time

Hawking lost the bet, conceding by breaking into Thorne’s office whilst he was on a trip to Russia and signing the framed bet.

The team now intend to apply the technique that led them to this finding to investigate further black holes. This should enable them to better understand how massive stars lose mass through stellar winds. With that said, as Cygnus X-1 is relatively unique in the Milky Way–as one of the few black holes so far detected in orbit with a massive companion star– Miller-Jones believes that they are unlikely to find any more binary systems in which the masses of the constituent star and black hole diverge so drastically from current estimates.

“Most excitingly for me, the advent of cutting-edge new telescopes such as the Square Kilometre Array radio telescope (SKA) will allow us to detect many more black holes, and study their properties, including how matter flows into and away from them, in more detail than ever before,” concludes Professor Miller-Jones. “It’s an exciting time to be in this field!”

Sources

Miller-Jones. J., Orosz. J. A., Mandel. I., ‘Cygnus X-1 contains a 21-solar mass black hole – implications for massive star winds,’ Science, [2021], [https://science.sciencemag.org/lookup/doi/10.1126/science.abb3363]

Rare prediction: Star collision will be visible with the naked eye in 2022

Some scientists have made an unprecedented prediction, claiming that a pair of stars in the constellation Cygnus will collide approximately in 2022, creating an explosion so bright it will be visible to the naked eye.

The stars expected to merge are located in the Cygnus constellation. Image via NASA.

Calvin College professor Larry Molnar worked with his students and researchers from the Apache Point Observatory (Karen Kinemuchi) and the University of Wyoming (Henry Kobulnicky) to make an unprecedented claim. He and his team believe that two stars he is monitoring in the constellation Cygnus will merge and explode in 2022 (give or take a year), lighting up in the sky.

“It’s a one-in-a-million chance that you can predict an explosion,” Molnar said of his bold prognostication. “It’s never been done before.”

It will be a very dramatic change in the sky, as anyone can see it,” Calvin College astronomer Larry Molnar told National Geographic. “You won’t need a telescope to tell me in 2023 whether I was wrong or I was right.”

If it does happen, then you should see it easily without a telescope or any other specialized tools.

“It will be a very dramatic change in the sky, as anyone can see it. You won’t need a telescope to tell me in 2023 whether I was wrong or I was right,” Molnar said at the presentation, according to National Geographic.

The two stars, jointly called KIC 9832227, are located 1,800 light years away from Earth. Astronomers expect them to merge at some point but the exact time is hard to predict. Stellar collisions occur about once every 10,000 years and scientists have only recently been able to observe a stellar merger. If we will see the explosion in 2022, then this means that they have already exploded for 1795 years, but light from them hasn’t reached us already. As we can see them, the stars are quite close to one another. Daniel Van Noord, who also worked on the study, said they share an atmosphere together “like two peanuts sharing a single shell.”

It was actually Van Noord who started the study in 2013, when he realized that the star (as astronomers considered it then) was actually a binary system.

“He looked at how the color of the star correlated with brightness and determined it was definitely a binary,” said Molnar. “In fact, he discovered it was actually a contact binary, in which the two stars share a common atmosphere, like two peanuts sharing a single shell.”

“From there Dan determined a precise orbital period from Kinemuchi’s Kepler satellite data (just under 11 hours) and was surprised to discover that the period was slightly less than that shown by earlier data” Molnar continued.”

This reminded them of the work of Romuald Tylenda, who made similar observations of a star in 2008. The star system exhibited a similar behavior and then exploded – prompting Molnar to believe that the same thing will happen here. Extrapolating the data from Tylenda’s study they made the bold prediction and even set a date for it: 2022.

A red nova explosion like the one we might expect in 2022. Image via Space Telescope Science Institute

Whether or not this will happen, we should pay close attention, Molnar says, because this event will broaden our understanding of stars.

“Bottom line is we really think our merging star hypothesis should be taken seriously right now and we should be using the next few years to study this intensely so that if it does blow up we will know what led to that explosion,” he says.

The study is interesting because unlike most astronomical observations, which involve numerous team and expensive equipment, this study was low-scale and low-cost, which is why Molnar can afford to make such a risky prediction, as he himself says.

“Most big scientific projects are done in enormous groups with thousands of people and billions of dollars,” he said. “This project is just the opposite. It’s been done using a small telescope, with one professor and a few students looking for something that is not likely.”

“Nobody has ever predicted a nova explosion before. Why pay someone to do something that almost certainly won’t succeed? It’s a high-risk proposal. But at Calvin it’s only my risk, and I can use my work on interesting, open-ended questions to bring extra excitement into my classroom. Some projects still have an advantage when you don’t have as much time or money.”