The Register Citizen (Torrington, CT)
Massive star photographed by an SCSU astronomer
You wouldn’t think that the most massive star in the sky would be hard to photograph. But what if its neighbor stars were also among the most massive stars and they all happened to be clustered together? Would your eyes, or camera, be able to distinguish between all those bright points of light?
Earlier this year a team of astronomers did just that using imaging techniques developed at Southern Connecticut University. They photographed R136, a bright cluster of stars in the southern constellation Dorado, producing the sharpest images produced to date. The images have helped scientists determine the mass of the most massive star yet discovered.
“It’s always been a sort of a question in star formation theory. What’s the upper limit?” said astronomer Elliot Horch of SCSU, who was on the research team that published the study. “It’s hard to simulate these very massive stars on a computer. So there’s still a lot we don’t know about them which is why observations are important.”
The study helps astronomers understand the extreme upper limits of star formation which helps scientists understand the lifecycle of stars and the evolution of the universe.
The beating heart of the Tarantula Nebula
The star cluster R136 contains the most massive star yet discovered, the creatively named R1361a. Between 150 and 200 times the size of the sun, the star burns brightly and intensely in a region of space populated by bright and intense stars. There are so many stars in the neighborhood that its difficult to distinguish between them.
“If you don’t have a good resolution image you wont be able to distinguish stars
that are close together,” said Horch. “They’ll blur together.”
To the eye in a telescope or binoculars the star cluster looks like a single bright point of light, surrounded by the luminous haze of the Tarantula Nebula. When R136 was first imaged, it was thought to be an object roughly one thousand times the size of the sun. It’s only more recent advances, like this one, that have let scientists see the individual stars of R136 clearly.
To compensate for this, Horch and his colleagues maximized the power of the Gemini South Zorro telescope in the mountains of Chile using a technique called speckle imaging. By taking many thousands of short exposure images and carefully processing them the team was able to compensate for the effect of the earth’s atmosphere. Horch is an expert at building camera systems for large telescopes.
“We used a camera I designed the optics for that is currently on the Gemini South telescope, one of the largest telescopes in the world,” said Horch.
Dr. Elena Sabbi, a star formation and stellar cluster evolution scientist at the
Space Telescope Science Institute, said that studies like this were important because they help researchers understand how stars are born and interpret what space-borne telescopes are seeing from galaxies even farther away.
“Look at the images from Webb (Space Telescope), in one or two pixels there might be 50, 60, even 100,000 stars,” said Dr. Sabbi. She said to correctly interpret those signals you needed good data on what radiation big stars emit. “All this information is based on what we can see in the local universe. It’s a really important test of that.”
The Tarantula Nebula is the largest stellar nursery in the night sky. The region is rich with hydrogen gas which condenses due to gravitational pressure. Thousands of stars have been born there often in quite proximity. If the Tarantula Nebula was as close to Earth as the Orion Nebula, a star-forming region in the Orion Constellation within our own galaxy, it would cover as much night sky as 75 full moons placed side to side and be bright enough to cast shadows.
The densest and brightest cluster of stars in the Tarantula
Nebula is R136, where the most massive star R136a1 was born.
R136 is also the closest starburst, a region of space containing dense stars, that experiences accelerated star formation, that we can observe from here on earth. Regions of space like this are very rare in our part of the universe.
“Our closest analog to R136 is a superstar cluster. We see superstar clusters in merging galaxies,” said Dr. Anna Rosen an expert in star formation at UC San Diego. Rosen pointed at the distant Antennae Galaxies which are in the process of falling into each other. “We know these regions of massive star formation are rare and they also tend to be extreme environments.”
The Milky Way is thought to be responsible for creating the extreme environment of the R136 cluster and the Tarantula Nebula. The nebula sits at the leading edge of of the Large Magellanic Cloud, a galaxy that orbits the Milky Way. This region of the LMC is where gravitational forces from the Milky Way compress the cold gasses into the dense Tarantula Nebula, creating the stellar nursery.
Think of it like two boats cutting through the water. The Milky Way generates a wake in the intergalactic medium. The LMC, also moving, is caught in our wake. Massive stars are born, and die where the LMC presses into our wake.
“Those massive stars are gonna die within a few million years,” said Rosen. She explained that they also dissipate the gasses that gave birth to them with their powerful solar winds. “Stars are their own worst enemies, once they start forming they push and heat the surrounding gas, quenching star formation.”
But in an environment like the Tarantula Nebula, enormous and dense with gas, those stellar winds create new, highly concentrated gas regions and promote new clusters of stars. Dr. Sabbi likened this to the bouncing of a pinball. Each molecule of gas zips through space, a pinball. Each stellar birth bounces and flips the balls again and again. The more bounces the more stars are born.
The stars of R136 ignited only a few million years ago. Life on Earth predates the birth of those stars. If dinosaurs cared to look at the night sky they would not have seen the stars of R136. Life has a good chance of outlasting those stars too. The bigger and hotter stars burn the faster they decay
“The bigger you are the faster you burn,” said Dr. Sabbi. “Very big stars last maybe three, four, five million years.”
Star forming regions like R136 don’t just make stars. Each star is a furnace that drives the formation of heavy elements. The building blocks of life, carbon, nitrogen and oxygen, are forged by nuclear fusion in the cores of these stars. When super-massive stars die as supernovas that violent end gives birth to heavy elements like gold, lead, copper and zinc. Studying regions of intense, massive, star formation gives astronomers clues into how fast elements form and how quickly the universe itself evolves.
Horch intends to use the imaging techniques developed for this study to study binary and trinary star systems, solar systems with multiple stars orbiting each other. Most stars, he explained, occur in pairs.
Horch hopes that he can share this exciting field with students at Southern Connecticut State University where he has taught for 15 years. He says that the physics department has been growing rapidly and competing with the likes of Yale, UConn, and Wesleyan in astronomy research.