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Unusually strong storm to grow into raging blizzard across U.S. Plains
Computer model simulation of the large, intense storm over the High Plains on March 13. Image: Earth Simulator A storm is forecast to move out of the Southwest and rapidly intensify over the plains of Colorado, Oklahoma and Kansas on Wednesday, bringing a wide array of life-threatening weather hazards for a large part of the country.
Why it matters: The storm is likely to intensify at a rate that will qualify it as a meteorological "bomb" — short for bombogenesis, which describes non-tropical storms whose central pressure drops by at least 24 millibars in 24 hours. In fact, this storm is likely to rival some of the most intense weather systems on record in parts of the Plains, as measured by its minimum central air pressure.
In general, the lower the pressure, the stronger the storm. While it isn't tropical in origin, this storm could have a minimum central air pressure that's typically found in a Category 2 hurricane. -
Nebulous, but no nebula
This Hubble Picture of the Week shows Messier 28, a globular cluster in the constellation of Sagittarius (The Archer), in jewel-bright detail. It is about 18 000 light-years away from Earth.
As its name suggests, this cluster belongs to the Messier catalogue of objects — however, when astronomer Charles Messier first added Messier 28 to his list in 1764, he catalogued it incorrectly, referring to it as a “[round] nebula containing no star”. While today we know nebulae to be vast, often glowing clouds of interstellar dust and ionised gases, until the early twentieth century a nebula represented any astronomical object that was not clearly localised and isolated. Any unidentified hazy light source could be called a nebula. In fact, all 110 of the astronomical objects identified by Messier were combined under the title of the Catalogue of Nebulae and Star Clusters. He classified many objects as diverse as star clusters and supernova remnants as nebulae. This includes Messier 28, pictured here — which, ironically, is actually a star cluster.
Messier’s mistake is understandable. Whilst Messier 28 is easily recognisable as a globular stellar cluster in this image, it is far less recognisable from Earth. Even with binoculars it is only visible very faintly, as the distorting effects of the Earth’s atmosphere reduce this luminous ancient cluster to a barely visible smudge in the sky. One would need larger telescopes to resolve single stars in Messier 28. Fortunately, from space Hubble allows Messier 28 to be seen in all its beauty — far more than a faint, shapeless, nebulous cloud.
Credit:
ESA/Hubble & NASA, J. E. Grindlay et al.
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Hubble & Gaia accurately weigh the Milky Way
In a striking example of multi-mission astronomy, measurements from the NASA/ESA Hubble Space Telescope and the ESA Gaia mission have been combined to improve the estimate of the mass of our home galaxy the Milky Way: 1.5 trillion solar masses.
The mass of the Milky Way is one of the most fundamental measurements astronomers can make about our galactic home. However, despite decades of intense effort, even the best available estimates of the Milky Way’s mass disagree wildly. Now, by combining new data from the European Space Agency (ESA) Gaia mission with observations made with the NASA/ESA Hubble Space Telescope, astronomers have found that the Milky Way weighs in at about 1.5 trillion solar masses within a radius of 129 000 light-years from the galactic centre.
Previous estimates of the mass of the Milky Way ranged from 500 billion to 3 trillion times the mass of the Sun. This huge uncertainty arose primarily from the different methods used for measuring the distribution of dark matter — which makes up about 90% of the mass of the galaxy.
“We just can’t detect dark matter directly,” explains Laura Watkins (European Southern Observatory, Germany), who led the team performing the analysis. “That’s what leads to the present uncertainty in the Milky Way’s mass — you can’t measure accurately what you can’t see!”
Given the elusive nature of the dark matter, the team had to use a clever method to weigh the Milky Way, which relied on measuring the velocities of globular clusters — dense star clusters that orbit the spiral disc of the galaxy at great distances [1].
“The more massive a galaxy, the faster its clusters move under the pull of its gravity” explains N. Wyn Evans (University of Cambridge, UK). “Most previous measurements have found the speed at which a cluster is approaching or receding from Earth, that is the velocity along our line of sight. However, we were able to also measure the sideways motion of the clusters, from which the total velocity, and consequently the galactic mass, can be calculated.” [2]
The group used Gaia’s second data release as a basis for their study. Gaia was designed to create a precise three-dimensional map of astronomical objects throughout the Milky Way and to track their motions. Its second data release includes measurements of globular clusters as far as 65 000 light-years from Earth.
"Global clusters extend out to a great distance, so they are considered the best tracers astronomers use to measure the mass of our galaxy" said Tony Sohn (Space Telescope Science Institute, USA), who led the Hubble measurements.
The team combined these data with Hubble’s unparalleled sensitivity and observational legacy. Observations from Hubble allowed faint and distant globular clusters, as far as 130 000 light-years from Earth, to be added to the study. As Hubble has been observing some of these objects for a decade, it was possible to accurately track the velocities of these clusters as well.
“We were lucky to have such a great combination of data,” explained Roeland P. van der Marel (Space Telescope Science Institute, USA). “By combining Gaia’s measurements of 34 globular clusters with measurements of 12 more distant clusters from Hubble, we could pin down the Milky Way’s mass in a way that would be impossible without these two space telescopes.”
Until now, not knowing the precise mass of the Milky Way has presented a problem for attempts to answer a lot of cosmological questions. The dark matter content of a galaxy and its distribution are intrinsically linked to the formation and growth of structures in the Universe. Accurately determining the mass for the Milky Way gives us a clearer understanding of where our galaxy sits in a cosmological context.
Notes
[1] Globular clusters formed prior to the construction of the Milky Way’s spiral disk, where our Sun and the Solar System later formed. Because of their great distances, globular star clusters allow astronomers to trace the mass of the vast envelope of dark matter surrounding our galaxy far beyond the spiral disk.
[2] The total velocity of an object is made up of three motions — a radial motion plus two defining the sideway motions. However, in astronomy most often only line-of-sight velocities are available. With only one component of the velocity available, the estimated masses depend very strongly on the assumptions for the sideway motions. Therefore measuring the sideway motions directly significantly reduces the size of the error bars for the mass.
More information
The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
ESA's Gaia satellite was launched in 2013 to create the most precise three-dimensional map of more than one billion stars in the Milky Way. The mission has release two lots of data thus far: Gaia Data Release 1 in 2016 and Gaia Data Release 2 in 2018. More releases will follow in the coming years.
The study was presented in the paper “Evidence for an Intermediate-Mass Milky Way from Gaia DR2 Halo Globular Cluster Motions”, which will be published in The Astrophysical Journal.
The international team of astronomers in this study consists of Laura L. Watkins (European Southern Observatory, Germany), Roeland P. van der Marel (Space Telescope Science Institute, USA, and Johns Hopkins University Center for Astrophysical Sciences, USA), Sangmo T. Sohn (Space Telescope Science Institute, USA), and N. Wyn Evans (University of Cambridge, UK).
Image credit: ESA/Hubble, L. Watkins, L. Calçada
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Dramatic Tilts May Define Many Alien Worlds
New research helps explain how dramatic tilts can influence exoplanets' orbits.(Image: © Sarah Millholland/NASA/JPL-Caltech)By Charles Q. Choi 21 hours ago Science & AstronomyMany alien planets around stars like our sun are potentially extraordinarily tilted, leading to dramatic swings between extreme winters and summers, a new study finds.
NASA's Kepler spacecraft revealed that about 30 percent of stars similar to our sun harbor super-Earths. As their name implies, super-Earths are a bit bigger than Earth, at about two to 10 times Earth's mass.
The super-Earths found so far also typically lie relatively near their stars, taking less than 100 days to complete an orbit, according to a statement on the new work. In comparison, Mercury takes about 88 days to go around the sun.
Related: The Most Fascinating Exoplanets of 2018
Oddly, many of these super-Earths are found almost — but not quite — in naturally stable relationships known as orbital resonances, which occur when orbiting bodies exert a regular gravitational influence on one another. For example, Pluto's and Neptune's orbital resonance lead Pluto to complete two laps around the sun in the time it takes Neptune to orbit three times. In contrast, many super-Earths are in pairs that are near, but not in, such orbital resonances.
Now researchers suggest the potential answer to this mystery is that such worlds are highly tilted. "If true, this implies that their seasons are extreme, and their weather and climates will be affected non-trivially as well," lead study author Sarah Millholland, an astronomer at Yale University in Connecticut, told Space.com.
Previous research suggested that when planets are close to coming into orbital resonance, the gravitational pull of their stars on these worlds can result in tidal forces that can drain energy away from their orbital motions, converting it to heat and keeping those worlds from synchronizing their orbits. However, prior work also found such tidal forces are not by themselves strong enough to prevent orbital resonance, the researchers said.
The scientists ran computer simulations modeling what happens when the poles of these planets are tilted with respect to their orbits. They found that with high axial tilts, tidal forces "are exceedingly more efficient at draining orbital energy into heat in the planets," Millholland said in the statement.
The greater the axial tilt, the more variation in how much sunlight different parts of a planet receive over the course of its year. Earth's axial tilt of about 23.5 degrees results in its seasons; Uranus' extreme axial tilt of 98 degrees leaves the winter side of the planet in complete darkness for 21 years and the summer side in constant daylight for the same amount of time.
"Up until now, the typical assumption was that close-in exoplanets have zero axial tilt," Millholland told Space.com. "Our study suggests otherwise."
The phenomenon the scientists discovered may also lead to extraordinary amounts of heating in these exoplanets. A similar effect results in Jupiter's moon Io "having extreme volcanic activity; it is the most geologically active body in the solar system," Millholland said.
The researchers "are not suggesting that spin poles of all exoplanets are highly tilted," Millholland noted. However, if a significant fraction are, that would explain why so many close-in super-Earths have the orbits that astronomers have detected, she said.
The scientists are now analyzing the ways in which heating related to high axial tilt may influence the structures of these planets, Millholland said. Exoplanets with high axial tilts should possess heat signatures detectable by future space missions, such as the James Webb Space Telescope, the researchers added.
The scientists detailed their findings online March 4 in the journal Nature Astronomy.
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Hubble & Gaia accurately weigh the Milky Way
In a striking example of multi-mission astronomy, measurements from the NASA/ESA Hubble Space Telescope and the ESA Gaia mission have been combined to improve the estimate of the mass of our home galaxy the Milky Way: 1.5 trillion solar masses.The mass of the Milky Way is one of the most fundamental measurements astronomers can make about our galactic home. However, despite decades of intense effort, even the best available estimates of the Milky Way’s mass disagree wildly. Now, by combining new data from the European Space Agency (ESA) Gaia mission with observations made with the NASA/ESA Hubble Space Telescope, astronomers have found that the Milky Way weighs in at about 1.5 trillion solar masses within a radius of 129 000 light-years from the galactic centre.
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Galactic Wind Provides Clues to Evolution of Galaxies
The magnetic field lines of the the Cigar Galaxy (also called M82) appear in this composite image. The lines follow the bipolar outflows (red) generated by exceptionally high rates of star formation. Credit: NASA/SOFIA/E. Lopez-Rodiguez; NASA/Spitzer/J. Moustakas et al. -
Colliding galaxies
Located in the constellation of Hercules, about 230 million light-years away, NGC 6052 is a pair of colliding galaxies. They were first discovered in 1784 by William Herschel and were originally classified as a single irregular galaxy because of their odd shape. However, we now know that NGC 6052 actually consists of two galaxies that are in the process of colliding. This particular image of NGC 6052 was taken using the Wide Field Camera 3 on the NASA/ESA Hubble Space Telescope.
A long time ago gravity drew the two galaxies together into the chaotic state we now observe. Stars from within both of the original galaxies now follow new trajectories caused by the new gravitational effects. However, actual collisions between stars themselves are very rare as stars are very small relative to the distances between them (most of a galaxy is empty space). Eventually things will settle down and one day the two galaxies will have fully merged to form a single, stable galaxy.
Our own galaxy, the Milky Way, will undergo a similar collision in the future with our nearest galactic neighbour, the Andromeda Galaxy. Although this is not expected to happen for around 4 billion years so there is nothing to worry about just yet.
This object was previously observed by Hubble with its old WFPC2 camera. That image was released in 2015.
Credit:
ESA/Hubble & NASA, A. Adamo et al.
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The bizarre and brilliant rules for naming new stuff in space
From left, Venus, the Moon and Jupiter are seen in the early morning sky near Salgotarjan, Hungary, on Jan. 31, 2019 (Peter Komka/APBy Sarah KaplanFebruary 27
Aspiring lunar explorers, take heed — any newly discovered ridges on the moon must be named for a geoscientist. If you want to name a landform on Saturn’s satellite Titan, you’d better be a fantasy or science fiction fan: Mountains and plains on the lake-covered moon are styled after places in Tolkien’s Middle Earth and Frank Herbert’s “Dune” series. And almost everything on Io, the eruptive moon of Jupiter, must have a name associated with fire, volcanoes, or Dante’s “Inferno.”
So decrees the International Astronomical Union, the official arbiter of planetary and satellite nomenclature since 1919. As ever more powerful telescopes and ambitious new robotic missions add to the identified real estate of the solar system, the IAU’s brilliant, byzantine and sometimes marvelously nerdy naming guidelines help bring order to our crowded skies.
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The two mysterious populations of NGC 2419
Globular clusters like NGC 2419, visible in this image taken with the NASA/ESA Hubble Space Telescope, are not only beautiful, but also fascinating. They are spherical groups of stars which orbit the centre of a galaxy; in the case of NGC 2419, that galaxy is the Milky Way. NGC 2419 can be found around 300 000 light-years from the Solar System, in the constellation Lynx (the Lynx).
The stars populating globular clusters are very similar to one another, with similar properties such as metallicity. The similarity of these stellar doppelgängers is due to their formation early in the history of the galaxy. As the stars in a globular cluster all formed at around the same time, they tend to display reasonably homogeneous properties. It was believed that this similarity also extended to the stellar helium content; that is, it was thought that all stars in a globular cluster would contain comparable amounts of helium.
However, Hubble’s observations of NGC 2419 have shown that this is not always the case. This surprising globular cluster turns out to be made up of two separate populations of red giant stars, one of which is unusually helium-rich. Other elements within the different stars in NGC 2419 vary too — nitrogen in particular. On top of this, these helium-rich stars were found to be predominantly in the centre of the globular cluster, and to be rotating. These observations have raised questions about the formation of globular clusters; did these two drastically different groups of stars form together? Or did this globular cluster come into being by a different route entirely?
Credit:
ESA/Hubble & NASA, S. Larsen et al.
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