When you hear the phrase “spiral arms” you probably think of galaxies. Lots of galaxies have bright arcs of stars that spiral away from their center, including our Milky Way. But not all galaxies have spiral arms, and galaxies aren’t the only celestial objects with spiral arms. About a third of protoplanetary disks around young stars have spiral arms, and we now think we know why.Continue reading “A Planet has Whipped Up Spiral Arms Around a Young Star”
Beginning in 1610, when famed Renaissance polymath Galileo Galilei observed the night sky using a telescope of his own manufacture, astronomers gradually realized that our Solar System is part of a vast collection of stars known today as the Milky Way Galaxy. By the 20th century, astronomers had a good idea of its size and structure, which consisted of a central “bulge” surrounded by an extended disk with spiral arms. Despite all we’ve learned, determining the true morphology of the Milky Way has remained a challenge for astronomers.
Since we, the observers, are embedded in the Milky Way’s disk, we cannot see through the center and observe what’s on the other side. Using various methods, though, astronomers are getting closer to recreating what a “birds-eye” view of the galaxy would look like. For instance, a team of researchers from the Chinese Academy of Sciences (CAS) used the precise locations of very young objects in our galaxy (for the first time) to measure the morphology of the Milky Way. This revealed a multiple-arm morphology consisting of two symmetrical arms in the inner region and many irregular ones in the outer region.Continue reading “What Does the Milky Way Look Like?”
Astronomers using the ALMA Observatory have discovered an unusual, massive star near the center of our galaxy, a star that has two spiral arms. The arms are part of an accretion disk, a broad disk of dust and gas surrounding the protostar. While this is not the first star to be seen with such rare arm-like features, researchers say they believe they can track the formation of the spiral arms to a close encounter the star had with another object.Continue reading “A Star has Grown Spiral Arms”
Astronomers have watched the young binary star system SVS 13 for decades. Astronomers don’t know much about how planets form around proto-binary stars like SVS 13, and the earliest stages are especially mysterious. A new study based on three decades of research reveals three potentially planet-forming disks around the binary star.Continue reading “Planets Have Just Started to Form in This Binary System”
Even after thirty years of faithful service, the Hubble Space Telescope continues to reveal truly fascinating things about our Universe. This includes the image (shown at top) taken of the astronomical feature known as NGC 2273, a barred spiral galaxy similar to the Milky Way. However, upon closer inspection, the image reveals that the spiral arms of this galaxy contain a second set of spiral arms.Continue reading “Hubble Sees a Galaxy With Spiral Arms, Surrounded by Other Spiral Arms”
Spiral galaxies are an iconic form. They’re used in product logos and all sorts of other places. We even live in one. And though it may seem kind of obvious how they get their shape, by rotating, that’s not the case.Continue reading “How Spiral Galaxies Get Their Shape”
How disk galaxies form their spiral arms have been puzzling astrophysicists for almost as long as they have been observing them. With time, they have come to two conclusions… either this structure is caused by differences in gravity sculpting the gas, dust and stars into this familiar shape, or its just a random occurrence which comes and goes with time.
Now researchers are beginning to wrap their conclusions around findings based on new supercomputer simulations – simulations which involve the motion of up to 100 million “stellar particles” that mimic gravitational and astrophysical forces which shape them into natural spiral structure. The research team from the University of Wisconsin-Madison and the Harvard-Smithsonian Center for Astrophysics are excited about these conclusions and report the simulations may hold the essential clues of how spiral arms are formed.
“We show for the first time that stellar spiral arms are not transient features, as claimed for several decades,” says UW-Madison astrophysicist Elena D’Onghia, who led the new research along with Harvard colleagues Mark Vogelsberger and Lars Hernquist.
“The spiral arms are self-perpetuating, persistent, and surprisingly long lived,” adds Vogelsberger.
When it comes to spiral structure, it’s probably the most widely occurring of universal shapes. Our own Milky Way galaxy is considered to be a spiral galaxy and around 70% of the galaxies near to us are also spiral structured. When we think in a broader sense, just how many things take on this common formation? Whisking up dust with a broom causes particles to swirl into a spiral shape… draining water invokes a swirling pattern… weather formations go spiral. It’s a universal happening and it happens for a reason. Apparently that reason is gravity and something to perturb it. In the case of a galaxy, it’s a giant molecular cloud – the star-forming regions. Introduced into the simulation, the clouds, says D’Onghia, a UW-Madison professor of astronomy, act as “perturbers” and are enough to not only initiate the formation of spiral arms but to sustain them indefinitely.
“We find they are forming spiral arms,” explains D’Onghia. “Past theory held the arms would go away with the perturbations removed, but we see that (once formed) the arms self-perpetuate, even when the perturbations are removed. It proves that once the arms are generated through these clouds, they can exist on their own through (the influence of) gravity, even in the extreme when the perturbations are no longer there.”
So, what of companion galaxies? Can spiral structure be caused by proximity? The new research also takes that into account and models for “stand alone” galaxies as well. However, that’s not all the study included. According to Vogelsberger and Hernquist, the new computer-generated simulations are focusing on clarifying observational data. They are taking a closer look at the high-density molecular clouds and the “gravitationally induced holes in space” which act as ” the mechanisms that drive the formation of the characteristic arms of spiral galaxies.”
Until then, we know spiral structure isn’t just a chance happening and – to wrap things up – it’s probably the most common form of galaxy in our Universe.
Original Story Source: Harvard-Smithsonian Center for Astrophysics.