Bad Astronomy | New image of star R136a shows it’s 200 times the mass of the sun

Huge stars – I mean really huge, 20 times the mass of the sun or more – are very powerful.

The energy they produce varies dramatically with mass, so at the top end of the range, stars can emit so much light that they can be seen in other galaxies with small telescopes and can bake any planet they have to a crisp. They can illuminate entire nebulae, and when they explode at the end of their short, intense lives, they can brighten entire galaxies.Milky Wayes plural.

But how big can stars get? This is an important question in astronomy. We have a good understanding of the behavior of stars like the Sun, but when you add more mass to them, their behavior becomes unstable.They can become unstable, pulsate and even explode only This side of a catastrophic supernova.

Furthermore, when massive stars explode, they seed the galaxies around them with heavy elements, such as iron, that they made during their lifetime. These elements are necessary to make planets and life. We do attribute our existence to supernova massive stars.

In theory, we want to know what the upper mass limit is, because it helps astronomers determine how stars are born and how they spend their lives.

Until recently, the limit was thought to be more than 300 times the mass of the sun, which is huge. But now, new observations of the most massive stars known suggest that may be an excess. The new results mean the mass limit is more like 200 solar masses.

The star is called R136a1. It is part of a very young, compact star cluster called NGC 2070 at the center of the Tarantula Nebula, a huge and spreading cloud of star-forming gas in a satellite galaxy of the Milky Way called the Large Magellanic Cloud. It’s about 160,000 light-years away.

Full observation of R136a1 is hardThe stars at the core of NGC 2070 are packed so tightly together that even with Hubble it would be difficult to separate them. This is critical; you can’t look at a star and figure out what it’s doing if its light is mixing with another nearby star.

To make it even better, a team of astronomers in Chile used the 8.1-meter Gemini South telescope, equipped with a special camera called Zorro [link to paper]. What’s special about it is that it can do speckle imaging.

Earth’s atmosphere is a pain for astronomers. It was in motion all the time, the air of the packet was pulled back and forth. Each of these acts like a lens, bending incoming light into stars. Over time, even for a fraction of a second, the image can move so much that it blurs into a circle that, oddly enough, is called the optic disc. Two or more stars that are close together in the sky can blend into a single blob.

One way to get around this is to take extremely short exposures, freezing the action. That’s what Zorro can do, taking an image in just 60 milliseconds. On Halloween 2021, astronomers took 40,000 such short exposures using several different filters to select certain star colors. They then moved and combined observations from each filter to negate the atmospheric dance that blurred them.

The larger the telescope, the better the resolution; that is, the closer two objects can be, and you can still separate them. Because Gemini is so large, using speckle imaging can get as good or better resolution than Hubble, which has a 2.4-meter mirror, but doesn’t have to deal with the atmosphere.

In the new image — the highest-resolution visible-light observation of the star ever made — R136a1 and dozens of stars around it are clearly seen. This allows astronomers to measure R136a1’s color better than ever before.

That part is critical. A star’s color can be compared to the expected color, given its properties: its mass, temperature, size, element abundance, age, etc.

All told, the new measurements put the giant star at 196 times the mass of the sun, with uncertainties of +34 and -27, so it could reasonably be between 169 and 230 times the mass of the sun. That’s an astonishing mass, but still well below the upper limit of nearly 300 solar masses previously estimated.

The astronomers working on the work cautioned that they pushed speckle imaging to the edge of what it could do, so they didn’t want to draw a line in the sand about mass. It’s still not sure. But it does suggest that since R136a1 is the most massive star known, the upper limit of stellar mass may be lower than thought.

By the way, this is the mass of the star now. It’s more than a million years old, and no doubt it lost a lot of mass to high winds during that time. Stars like these, known as Wolf-Rayet stars, blow away massive amounts of matter. So it used to be bigger. Just how big it is is unknown.

By the way, the luminosity they get for the star is 4.6 million several times that of the sun. If you replaced the sun with R136a1, it would look as big as your outstretched fist, but it would be so bright that your fist would catch fire and the earth would scorch. Yes. Luckily it’s a few galaxies away from us.

It also changed the way we think about some stellar explosions.Supermassive stars can undergo a theoretical type of explosion called unstable supernova, which could lead to a superluminous explosion. However, if the upper limit of the mass of stars was 200 instead of 300 solar masses, then the number of such supernovae we might see would be reduced. In addition, the amount of heavy elements blasted out by supermassive stars is largely dependent on mass, so this new result could change how we think about all of these key elements.

This is not some esoteric result. It literally changed the way we see the universe and our origins in it.

So how can this new result be confirmed or disproved? Higher resolution, which means larger telescopes, at least in the 30-meter range. These don’t exist yet, but there are plans to build them. It’s going to be a while, though, so now astronomers will have to come up with other ways to study the universe’s largest stellar beast.

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