This mountain of interstellar gas and dust lies in the picturesque Eagle Nebula. Though it appears solid in this near-infrared image from JWST, the density of the structure is actually quite low. Jets and solar winds from the glowing, young stars inside the region sculpt the pillar’s shape. Over the next 100,000 years, the stars’ energetic jets, solar winds, and destructive supernovas will destroy the dusty nursery. (Image credit: NASA/ESA/CSA/STScI/M. Özsaraç)
Tag: stars
Betelgeuse’s Flickering
Between November 2019 and March 2020 Betelgeuse, the red supergiant star in the constellation Orion’s left shoulder, experienced what’s being called the Great Dimming. Usually, the star is one of the ten brightest stars in the sky, often visible even in the suburban sprawl. But as of February 2020, it had dimmed by a factor of 2.5.
Observers speculated all sorts of causes, including the idea that this was a precursor to a supernova explosion. Instead, it’s a relatively normal occurrence for a star like Betelgeuse. The image above is from a numerical simulation of the star, and it shows approximately what it would look like to the human eye over a 7.5 year time span. As you can see, its brightness varies noticeably, and its surface seems almost to boil. This has to do with convection in the star. Compared to a star like our sun, Betelgeuse has fewer — and much larger — convection cells.
With a little more time and data, astronomers pinned down the exact source of Betelgeuse’s flickering during the Great Dimming. The year before the star belched an enormous bubble of gas into space. Then, when part of the star cooled in the aftermath, that gas condensed and formed a dust cloud which partially obscured the star. You can see an artist’s conception of the situation in the video below. (Image and research credit: B. Freytag; research credit: M. Montargès et al.; video credit: ESO/L. Calçada)
Understanding Stars’ Seismology
Our understanding of Earth’s interior is based mostly on observations of seismic waves, which travel differently through our rocky crust and the molten core. Scientists similarly use seismic waves in stars to determine their interiors. But the pressure and temperature conditions in stars are far beyond anything we have here on Earth, which makes predicting how waves will travel in such exotic material difficult.
To better understand these extreme temperatures and pressures, scientists are using Lawrence Livermore’s National Ignition Facility (NIF) to mimic conditions similar to the outer envelope of a white dwarf star, like the one shown in the center of the image above. NIF’s laser array – shown as the blue lines in the artist’s conception above – can generate spherical shock waves that, as they converge on a solid sample, create pressures as high as 450 Mbar, more than 400 million times sea level atmospheric pressure here on Earth. Although the shock wave takes only 9 ns to travel across the sample, it’s enough to give researchers a glimpse into star-like conditions. (Image credit: NASA/ESA/C. O’Dell/D. Thompson, Lawrence Livermore National Laboratory; via Physics Today)
Stellar Bow Shock
This Hubble image shows a young star in the Orion Nebula and the curved bow shock arcing around it. Despite its age, the star LL Orionis is energetic, producing a stellar wind that exceeds our sun’s. When that wind collided with the flow in the Orion Nebula, it formed this bow shock that is about a half a light-year wide. We don’t often think about fluid dynamics applying in space, but if we consider a lengthscale that is large enough, even space contains enough matter to behave like a fluid. LL Orionis’s bow shock is in many ways comparable to ones we see form around re-entering spacecraft. (Image credit: NASA/Hubble, via APOD; submitted by jshoer)
Supernova Simulation
New research shows that supermassive first-generation stars may explode in supernovae without leaving behind remnants like black holes. The work is a result of modeling the life and death of stars 55,000 to 56,000 times more massive than our sun. When such stars reach the end of their lives, they become unstable due to relativistic effects and begin to collapse inward. The collapse reinvigorates fusion inside the star and it begins to rapidly fuse heavier elements like oxygen, magnesium, or even iron from the helium in its core. Eventually, the energy released overcomes the binding energy of the star and it explodes outward as a supernova. The image above is a slice through such a star approximately one day after its collapse is reversed. Hydrodynamic instabilities like the Rayleigh-Taylor instability produce mixing of the heavy elements throughout the expanding interior of the star. The mixing should produce a signature that can be observed in the aftermath as these stars seed their galaxies with the heavy elements needed to form planets. For more, see Science Daily and Chen et al. (Image credit: K. Chen et al., via Science Daily; submitted by mechanicoolest)
Astronomical Jets
Researchers have pieced together Hubble images of jets from newborn stars into timelapse movies that reveal the interstellar fluid mechanics responsible for the formation of stars like our sun. These jets stream out clumps of matter that has fallen on the new star. When faster moving eddies impact slower ones, bow shocks can form, much like shockwaves running before an airplane. See more HD video of these jets and bow shocks here. #
