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Tag Archives: Milky Way

Astronomers from the International Centre for Radio Astronomy Research (ICRAR), in Perth in Western Australia, have produced what they call the GLEAMoscope to enable you to view the Milky Way over many different wavelengths, from gamma-ray to radio. (The name ‘GLEAM’ is derived from GaLactic and Extragalactic All-Sky Murchison Widefield Array.)

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Credit: Natasha Hurley-Walker/GLEAM team

 

The plane of the Milky Way is shown as the horizontal across the middle. The north pole of the Galaxy is towards the top. Go to the GLEAMoscope website and use the sliding bar at the top left of the to change the wavelengths shown. (Note the image above is just a still and is not interactive.)  Different wavelengths reveal different features, from the dull red glow of hydrogen gas permeating through space, to the stars and dust clouds of our visible galaxy, and superhot gas generating x-rays.

Link: GLEAMoscope.

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From an ESA press release, September 14, 2016 :

The first catalogue of more than a billion stars from ESA’s Gaia satellite was published on September 14, 2016 – the largest all-sky survey of celestial objects to date.

On its way to assembling the most detailed 3D map ever made of our Milky Way galaxy, Gaia has pinned down the precise position on the sky and the brightness of 1.142 billion stars. As a taster of the richer catalogue to come in the near future, this data release also features the distances and the motions across the sky for more than two million stars.

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Credit: ESA/Gaia/DPAC

The map projection above shows an all-sky view of stars in the Milky Way and our neighboring galaxies, based on the first year or so of Gaia’s observations. It shows the density of stars observed by Gaia in each portion of the sky. Brighter regions indicate denser concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed. Darker regions across the Galactic Plane correspond to dense clouds of interstellar gas and dust that absorb starlight along the line of sight. Many globular and open clusters – groupings of stars held together by their mutual gravity – are also sprinkled across the image.

Note that the faint curved features and dark stripes are not of astronomical origin but rather reflect Gaia’s scanning procedure. As this map is based on observations performed during the mission’s first year, the survey is not yet uniform across the sky. These artefacts will gradually disappear as more data are gathered during the five-year mission.

Links: ESA press release, Gaia sky map.

From a press release of the Max Planck Institute for Radio Astronomy, April 21, 2015:

Joint observations by the Atacama Pathfinder Experiment (APEX) telescope in Chile and Antarctica’s largest astronomical telescope come closer to making detailed images of the supermassive black hole in the centre of the Milky Way, up to its very edge, the “event horizon”. These successful observations were conducted within the framework of the Event Horizon Telescope – a virtual telescope as big as planet Earth.

Event Horizon Telescope

Credit: © Dan Marrone/University of Arizona

The South Pole Telescope (SPT) and APEX joined together in a ‘Very Long Baseline Interferometry’ experiment for the first time in January 2015. The two telescopes together observed two sources — the black hole at the centre of the Milky Way galaxy, Sagittarius A*, and the black hole at the centre of the nearby galaxy Centaurus A — and combined their signals to synthesize a telescope 7,000 kilometres across. With this success, the SPT joins the Event Horizon Telescope array, which connects APEX, the Large Millimeter Telescope in Mexico, the Submillimeter Telescope in Arizona, the Combined Array for Research in Millimeter-wave Astronomy in California, the Submillimeter Array and James Clerk Maxwell Telescope in Hawaii, and the Institute for Radio Astronomy Millimetrique (IRAM) telescopes in Spain and France.

Even though the Milky Way’s black hole is 4 million times more massive than the Sun, it is tiny to the eyes of astronomers. Smaller than Mercury’s orbit around the Sun, yet almost 26,000 light years away, studying its event horizon in detail is equivalent to standing in New York and reading the date on a cent in Germany.

With its unprecedented resolution, more than 1,000 times better than the Hubble Telescope, the EHT will see swirling gas on its final plunge over the event horizon, never to regain contact with the rest of the universe. If the theory of general relativity is correct, the black hole itself will be invisible because not even light can escape its immense gravity. However, it might still be seen as a silhouette against the background.

Links: MPIfR press release; EHT home.

Adapted from a UCLA press release, November 3, 2014.

For years, astronomers have been puzzled by a bizarre object in the center of the Milky Way that was believed to be a hydrogen gas cloud headed toward our galaxy’s enormous black hole. (See Section 15.5, Chapter opener figure, p. 382, and Figure 15-5, p. 388.)

Having studied it during its closest approach to the black hole this summer, UCLA astronomers believe that they have solved the riddle of the object widely known as G2.

A team led by Andrea Ghez determined that G2 is most likely a pair of binary stars that had been orbiting the black hole in tandem and merged together into an extremely large star, cloaked in gas and dust – its movements choreographed by the black hole’s powerful gravitational field. The research is published today in the journal Astrophysical Journal Letters.

Astronomers had figured that if G2 had been a hydrogen cloud, it could have been torn apart by the black hole, and that the resulting celestial fireworks would have dramatically changed the state of the black hole. However, G2 survived and continues on its orbit unaffected.

G2 appears to be just one of an emerging class of stars near the black hole that are created because the black hole’s powerful gravity drives binary stars to merge into one. In our galaxy, massive stars primarily come in pairs. The star suffered an abrasion to its outer layer but otherwise will be fine.

Keck Observatory

Credit and copyright: Ethan Tweedie Photography

The team utilized the Keck Observatory’s adaptive optics technology, a powerful technology that corrects the distorting effects of the Earth’s atmosphere in real time to more clearly reveal the space around the supermassive black hole.

Links: full UCLA press release, Keck press release.

Adapted from a press release of the Royal Astronomical Society (RAS):

A team of international astronomers has created a detailed three-dimensional map of the dusty structure of the Milky Way, as seen from Earth’s northern hemisphere.

3D map, detail

Credit: Sale et al./IPHAS

Dust and gas, which make up the interstellar medium (ISM), fill the space between stars in galaxies. The dust in the ISM is shaped by turbulent flows that form intricate fractal structures on scales ranging from thousands of light years down to hundreds of kilometers. Rather than measuring the dust itself to create the map, the team has used observations of more than 38 million stars to estimate how much starlight has been obscured by the ISM and thus how much dust lies in our line of sight to each star. This ‘extinction’ map derives from the newly released catalog of the Isaac Newton Telescope Photometric H-alpha Survey of the Northern Galactic Plane (IPHAS), the first digital survey to cover the entire northern Milky Way.

The map shows how extinction builds with distance away from the Sun (typically out to 12,000 light years or more) in any part of the surveyed northern Milky Way. The fractal nature of the ISM is visible in the map, as are large-scale features, such as star-forming molecular clouds and bubbles of ionized gas around clusters of hot stars.

Links: Full RAS press release; IPHAS homepage for map downloads (large file sizes) c/o Stuart Sale, University of Oxford.

In Chapter 15 (the opening photo, p. 382, and Figure 15-15d, p. 395), we discuss the prospective effect of a gas cloud called G2 (“G” for “gas”) that was heading for the center of the Milky Way, perhaps dropping material in to the supermassive black hole known as Sagittarius A* (pronounced A-star) and causing it to flare brightly in x-rays and radio waves, at least. But the prediction for its closest approach is about now, mid-2014, and no brightening has apparently happened. It is still possible that there could be dramatic flaring in the future, but that could be years or decades off.

Credit: ESO

Credit: ESO

Scientists at the Max-Planck Institute for Extraterrestrial Physics in Germany base it on their observations with the European Space Agency’s Very Large Telescope. They suggest that “G2 may be a bright knot in a much more extensive gas streamer.”

Daryl Haggard, who has recently moved to Amherst College from Northwestern University, is lead author of a report of Chandra X-ray Observatory monitoring of “Sgr A*/G2” through six observations in the first half of 2014, including the predicted time of the closest encounter.

These articles describing the situation is available free online, and the main results are discussed by correspondent Ron Cowen in The New York Times for July 22, 2014.

Links: NY Times article by Cowan; the original ApJ article by Oliver Pfuhl, Stefan Gillessen, and a dozen others; Daryl Haggard’s report, from The Astronomer’s Telegram.

A reference to a photo of the Spitzer Space Telescope now goes to an updated photo showing the Herschel Space Telescope, so:
on p. 391, column 2, line –2, “(Section 3.8c, Figure 3–32a)” for Spitzer should say simply “(Section 3.8c)”;
on p. 392, column 1, line 5, add: “(See Section 3.8c, Figure 3–32a.)”.

Clarification of Figure 15-11 on p. 392:
Note that strips (a) through (m) are organized top to bottom.

The Fermi Gamma-ray Space Telescope celebrates 2000 days of orbiting Earth this week with a new map of the gamma-ray sky, published on APOD on December 6, 2013.

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Credit: International Fermi Large Area Telescope Collaboration, NASA, DOE

For an Earth-orbiting gamma-ray telescope, Earth is actually the brightest source of gamma-rays, the most energetic form of light. Gamma-rays from Earth are produced when high energy particles, cosmic rays from space, crash into the atmosphere. While that interaction blocks harmful radiation from reaching the surface, those gamma-rays dominate in this remarkable Earth and sky view from the orbiting Fermi Gamma-ray Space Telescope’s Large Area Telescope. The image was constructed using only observations made when the center of our Milky Way galaxy was near the zenith, directly above the Fermi satellite. The zenith is mapped to the center of the field. The Earth and points near the nadir, directly below the satellite, are mapped to the edges of the field resulting in an Earth and all-sky projection from Fermi’s orbital perspective. The color scheme shows low intensities of gamma-rays as blue and high intensities as yellowish hues on a logarithmic scale. Our fair planet’s brighter gamma-ray glow floods the edges of field, the high intensity yellow ring tracing Earth’s limb. Gamma-ray sources in the sky along the relatively faint Milky Way stretch diagonally across the middle.

Scientists at the Max Planck Institute for Extraterrestrial Physics in Germany have produced the first detailed three-dimensional map of the stars that form the inner regions of our Milky Way, the nuclear bulge (see p. 389).

Credit: ESO/NASA/JPL-Caltech/M. Kornmesser/R. Hurt

Using publicly available data from ESO’s VISTA survey telescope in Chile, the team found a peanut-shaped bulge with an elongated bar and a prominent X-structure, which had been hinted at in previous studies. This indicates that the Milky Way was originally a pure disk of stars, which then formed a thin bar, before buckling into the boxy peanut shape seen today.

The scientists expect that this measurement of the three-dimensional density of the bulge will help to constrain galaxy evolution models for both our Milky Way and spiral galaxies in general. It will also support a number of further studies on different stellar populations, gas flows, or microlensing.

Read the MPE press release and the ESO press release for more images and a movie simulation of the bulge rotating. The research is published as “Mapping the three-dimensional density of the Galactic bulge with VVV red clump stars” by C. Wegg et al. in the Monthly Notices of the Royal Astronomical Society.

Recent observations from April this year of the galactic center have revealed that parts of the in-falling gas cloud, which was detected in 2011, have already swung past the black hole at the heart of our Milky Way. Due to the tidal force of the gravity monster, the gas cloud has become further stretched, with its front moving now already 500 km/s faster than its tail. This confirms earlier predictions that its orbital motion brings it is close to the black hole, that it will not survive the encounter. With the new, detailed, observations the astronomers from the Max Planck Institute for Extraterrestrial Physics (MPE) can now also place new constraints the origins of the gas cloud, making it increasingly unlikely that it contains a faint star inside, from which the cloud might have formed.

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Credit: ESO/MPE/Marc Schartmann

The full article, with accompanying graphics, may be found here.