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galactic dust to 500 pc

This complex map (click for a closer look) shows the locations of dust in our galaxy, as measured out to a distance of 500 pc (roughly 1,630 light-years). Dust reveals important information about galactic structure and star formation — but it can also present a hindrance, dimming and reddening faraway sources. To correctly interpret distant observations, we need an accurate picture of how dust is distributed within our galaxy. A team of scientists led by Gregory Green (Stanford University; Max Planck Institute for Astronomy, Germany) have now built a detailed three-dimensional map of dust reddening in our galaxy out to a distance of a few kiloparsecs (~10,000 light-years). The authors accomplished this by using Gaia parallaxes and stellar photometry from Pan-STARRS 1 and 2MASS to infer the distances, reddenings, and types of 799 million stars. Their 3D map and data are freely accessible for use; for more information, see the article linked below.

Bonus

Check out the authors’ video, which reveals the 3D-ness of the dust distribution as the virtual camera orbits on a 25-pc loop around the Sun.

Citation

“A 3D Dust Map Based on Gaia, Pan-STARRS 1, and 2MASS,” Gregory M. Green et al 2019 ApJ 887 93. doi:10.3847/1538-4357/ab5362

NGC 1068

Editor’s note: AAS Nova will be on vacation for the remainder of this week. Our regular posting schedule will resume on Jan 21.

NGC 1068 SOFIA/HST

The magnetic field lines from SOFIA/HAWC+’s observations are here shown overplotted on this Hubble image of NGC 1068. [Lopez-Rodriguez et al. 2019]

This cryptic image is the (false-color) view of a large spiral galaxy, NGC 1068, at the far-infrared wavelength of 89 μm (click for the full view). The tiny hairs threading the galaxy show the magnetic field lines — ordinarily invisible — that pervade interstellar space. This magnetic field has been imaged using the HAWC+ instrument on SOFIA, a telescope that points out of a Boeing 747 airplane, observing above 99% of the Earth’s infrared-blocking atmosphere. HAWC+ has captured not only the infrared flux of the thermally emitting dust in NGC 1068, but also the polarization of the dust, which tells us what direction the magnetic field points at each location. By piecing this information together, a team led by Enrique Lopez-Rodriguez (SOFIA Science Center) has determined the overall structure of NGC 1068’s magnetic field, finding that it closely traces all the way along the spiral arms of the galaxy (24,000 light-years across!). To learn more about the authors’ results, check out the original article below.

Citation

“SOFIA/HAWC+ Traces the Magnetic Fields in NGC 1068,” Enrique Lopez-Rodriguez et al 2020 ApJ 888 66. doi:10.3847/1538-4357/ab5849

Hevelius's observatory

sunspot observations

Example page of Selenographia with a sunspot drawing made by Hevelius in September 1643. [Carrasco et al. 2019; Selenographia, courtesy of the Library of the Astronomical Obs. of the Spanish Navy]

Click on the image above to see the full view of the observatory of Johannes Hevelius, a Polish astronomer who lived in the 1600s. This print is found in Hevelius’s book Selenographia and is reproduced courtesy of the Library of the Astronomical Observatory of the Spanish Navy in a recent solar activity research study led by Victor Carrasco (University of Extremadura, Spain and Southwest Research Institute). Hevelius used his observatory to chart daily observations of sunspots (note, in the above image, the projection of the Sun’s disk from the telescope coming through the left wall onto a vertical screen at the right). His records from 1642 to 1645 are the only systematic sunspot observations we have from just before the Maunder Minimum, a prolonged period of reduced solar activity between 1645 and 1715. Carrasco and collaborators have now reevaluated Hevelius’s observations, using them to explore the first hints of this quiet time for the Sun. For more information, check out the original article below.

Citation

“Sunspot Characteristics at the Onset of the Maunder Minimum Based on the Observations of Hevelius,” V. M. S. Carrasco et al 2019 ApJ 886 18. doi:10.3847/1538-4357/ab4ade

NGC 6814

NGC 6814

Locations of the 90 Cepheids used to measure the distance to NGC 6814 are marked with magenta circles. [Bentz et al. 2019]

This stunning composite Hubble photograph (credited to Judy Schmidt; click for the full 2.6’ x 2.6’ view) reveals a nearby Seyfert galaxy, NGC 6814. How do we determine the distances to galaxies like this one? One approach is to use variable stars known as Cepheids. Cepheids have a direct relationship between their luminosity and pulsation period, so if we observe a sample of Cepheids in a galaxy, we can use their pulsations to infer the distance to that galaxy. A team of scientists led by Misty Bentz (Georgia State University) recently used Hubble imaging to identify 90 excellent Cepheid candidates in NGC 6814, allowing them to estimate a precise distance to the galaxy. They find it to be just a brief hop away (relatively speaking): roughly 71 million light-years. To learn more about the authors’ study, check out the original article below.

Citation

“A Cepheid-based Distance to the Seyfert Galaxy NGC 6814,” Misty C. Bentz et al 2019 ApJ 885 161. doi:10.3847/1538-4357/ab48fb

jellyfish galaxy

Feeling jelly? This detailed image (click for a wider view) reveals the molecular gas in the long tail of the jellyfish galaxy ESO 137-001. In this image, red emission is molecular gas newly detected with the Atacama Large Millimeter/submillimeter Array (ALMA), green shows MUSE Hα emission, and the background image (blue, green, and red) shows the galaxy as imaged by the Hubble Space Telescope. This jellyfish galaxy is located 220 million light-years away in the Norma galaxy cluster, and its tail is caused by ram pressure stripping — the stripping of its gas as the galaxy falls through the surrounding intracluster medium, the material that lies in the space between galaxies. In a new publication led by Pavel Jáchym (Astronomical Institute, Czech Academy of Sciences), astronomers present ALMA’s unprecedented high-resolution maps of this jellyfish galaxy’s molecular-gas tail and show how this helps us to understand star formation in these dynamic, intense environments. To learn more about star formation in cosmic jellyfish (and to view the full original image), check out the article below.

Citation

“ALMA Unveils Widespread Molecular Gas Clumps in the Ram Pressure Stripped Tail of the Norma Jellyfish Galaxy,” Pavel Jáchym et al 2019 ApJ 883 145. doi:10.3847/1538-4357/ab3e6c

hydrocarbons in Titan's atmosphere

This illustration shows some of the molecules that have been discovered in the hazy atmosphere of Saturn’s largest moon, Titan. Though nearly 98% of Titan’s stratosphere is molecular nitrogen, there’s just enough methane — CH4 — for some interesting chemistry to happen when ultraviolet light is thrown into the mix. After this light breaks apart the methane molecules, complex hydrocarbons can form as these newly freed fragments link together in chains. A team of scientists led by Nicholas Lombardo (U. of Maryland, NASA Goddard SFC, Yale U.) has now made the first unambiguous detection on Titan of a hydrocarbon known as propadiene (CH2CCH2; also called allene). This colorless, flammable gas had, before now, never been detected beyond Earth. Scientists believe that Titan’s atmosphere may resemble Earth’s primordial atmosphere, so understanding its component molecules is an important step to learn more about how our own planet evolved. To read more, check out the original article below.

Citation

“Detection of Propadiene on Titan,” Nicholas A Lombardo et al 2019 ApJL 881 L33. doi:10.3847/2041-8213/ab3860

ion loss and magnetic obliquities

How does tilting a planet affect its ability to hold on to its atmosphere in the face of intense stellar radiation? The above images are from a series of numerical simulations run by a team of scientists led by Chuanfei Dong (Princeton University), which explore the role of magnetic obliquity — the tilt of the planet’s magnetic field — in regulating the loss of ions from an exoplanet’s atmosphere. In particular, Dong and collaborators modeled Earth-like planets in the habitable zones of two different host stars: a Sun-like G dwarf (top row) and a TRAPPIST-1-like M dwarf (bottom row). The simulation frames above show the ion loss from these two planets with four different tilts: 0°, 45°, 90°, and 135° (columns from left to right). While obliquity doesn’t much affect mass loss for a planet around a Sun-like star, the planet around the M-dwarf loses twice as much mass when its obliquity is oriented at 90° than it does when it’s aligned at 0° — which could matter for such a planet’s potential habitability! For more information on the authors’ conclusions, check out the article below.

Citation

“Role of Planetary Obliquity in Regulating Atmospheric Escape: G-dwarf versus M-dwarf Earth-like Exoplanets,” Chuanfei Dong et al 2019 ApJL 882 L16. doi:10.3847/2041-8213/ab372c

disk dominated galaxy

What drives galaxies into different shapes and structures? To answer this question, we have to understand how the different components of galaxies form. In general, galaxies are made up of two main parts that form in different ways: a thin disk of stars, gas, and dust; and a thick spheroid of stars comprising a dense bulge and sparser halo. In a new study led by Min-Jung Park (Yonsei University, Republic of Korea), a team of scientists used a high-resolution cosmological simulation to explore these components of massive galaxies in more detail. In the image above, you’re seeing two views — face-on (top) and edge-on (bottom) — of a simulated massive, disk-dominated spiral galaxy. The left-most panels show the whole galaxy; the middle and right panels show the galaxy deconstructed into its spheroid (middle) and disk (right) components. By looking at these components separately, Park and collaborators are able to learn more about the processes that form these different parts of galaxies, shedding light on what causes galaxies’ final structures. To learn more about the authors’ conclusions, check out the article below.

Citation

“New Horizon: On the Origin of the Stellar Disk and Spheroid of Field Galaxies at z = 0.7,” Min-Jung Park et al 2019 ApJ 883 25. doi:10.3847/1538-4357/ab3afe

silicate grains

How do molecules form in the hostile environments of the circumstellar and interstellar medium? Laboratory experiments are helping us to better understand this process! The image above (click for the full view) shows a high-resolution electron microscopy image of the complex surfaces of silicate grains, representative of dust grains found in the space around and between stars. In a new study led by Alexey Potapov (Max Planck Institute for Astronomy, Germany), scientists deposited thin layers of carbon dioxide and ammonia ices on nanometer-sized silicate and carbon grains and explored the subsequent chemical reactions under conditions similar to those of the interstellar medium. In the team’s experiments, the reactions that form complex organic molecules happened three times as fast in the ice on the surface of dust grains as they did in the ice alone. This catalytic effect of dust surfaces is an important piece in the puzzle of how complex molecules — and ultimately, life — formed in our universe. You can read the full article below to find out more!

Citation

“Evidence of Surface Catalytic Effect on Cosmic Dust Grain Analogs: The Ammonia and Carbon Dioxide Surface Reaction,” Alexey Potapov et al 2019 ApJL 878 L20. doi:10.3847/2041-8213/ab2538

Uranus ring

This remarkable image of Uranus, taken at 3.1 mm with the Atacama Large Millimeter/submillimeter Array (ALMA), reveals thermal emission from the dust that makes up Uranus’s narrow ring system (Uranus itself is masked because it’s so bright compared to the rings). We know that Uranus’s rings are made up of centimeter- to meter-sized particles, but little is known about the composition, mass, or the detailed size distribution of these particles or the amount dust in between them. In a new study led by Edward Molter (University of California, Berkeley), a team of scientists presents ALMA and Very Large Telescope observations of the rings’ thermal emission for the first time. These observations indicate that Uranus’s epsilon ring — the primary ring — is devoid of dust. This stands in stark contrast to the rings around Saturn or Jupiter, for instance, which contain lots of micrometer-sized dust — raising the question of why Uranus’s epsilon ring is so unusual! For more information, check out the article below.

Citation

“Thermal Emission from the Uranian Ring System,” Edward M. Molter et al 2019 AJ 158 47. doi:10.3847/1538-3881/ab258c

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