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Category Archives: 15. The Milky Way: our home in the Universe

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.

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The European Space Agency’s billion-star surveyor, Gaia was launched into space on Thursday December 19, 2013, where it will embark on its mission to create a highly accurate 3D map of our galaxy. (See pp. 285, 290.)

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Credit: ESA

By repeatedly observing a billion stars, with its billion-pixel video camera, the Gaia mission will allow astronomers to determine the origin and evolution of our galaxy whilst also testing gravity, mapping our inner Solar System, and uncovering tens of thousands of previously unseen objects, including asteroids in our Solar System, planets around nearby stars, and supernovae in other galaxies.

Gaia will map the stars from an orbit around the Sun, near a location some 1.5 million km beyond Earth’s orbit known as the L2 Lagrangian point. The spacecraft will spin slowly, sweeping its two telescopes across the entire sky and focusing their light simultaneously onto a single digital camera, the largest ever flown in space. The ‘eye’ of Gaia’s camera has the most sensitive set of light detectors ever assembled for a space mission.

Once Gaia starts routine operations, in late Spring 2014, astronomers will have the challenge of dealing with a flood of data. Even after being compressed by software, the data produced by the five-year mission will fill over 30,000 CD-ROMs!

The first Gaia science is expected to be discoveries of new sources – supernovae, extreme variable stars, and blazars.

Links: University of Leicester press release; ESA launch campaign blog and press release; ESA lift-off movie.

The European Research Council (ERC) has awarded 14 million euros (around $19 million) to a team of European astrophysicists to construct the first accurate image of a black hole. The team will test the predictions of current theories of gravity, including Einstein’s general theory of relativity. The funding is provided in the form of a synergy grant, the largest and most competitive type of grant of the ERC. This is the first time an astrophysics proposal has been awarded such a grant.

The team, led by investigators at the University of Nijmegen, the Max Planck Institute for Radio Astronomy, and Goethe University in Frankfurt, hopes to measure the shadow cast by the event horizon of the black hole in the center of the Milky Way, find new radio pulsars near this black hole, and combine these measurements with advanced computer simulations of the behavior of light and matter around black holes as predicted by theories of gravity. They will combine several telescopes around the globe to peer into the heart of our own galaxy, which hosts a mysterious radio source called Sagittarius A* which is considered to be the central supermassive black hole. (See p. 383 and Section 15.5, p. 391.)

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Credit and © M. Moscibrodzka & H. Falcke, Radboud-Universität Nijmegen

Black holes are notoriously elusive with a gravitational field so large that even light cannot escape their grip. The team plans to make an image of the event horizon – the border around a black hole which light can enter, but not leave.  The scientists want to peer into the heart of our own galaxy, which hosts a mysterious radio source called Sagittarius A*. The object is known to have a mass of around 4 million times the mass of the Sun and is considered to be the central supermassive black hole of the Milky Way.

As gaseous matter is attracted towards the event horizon by the black hole’s gravitational attraction, strong radio emission is produced before the gas disappears. The event horizon should then cast a dark shadow on that bright emission. Given the huge distance to the center of the Milky Way, the shadow is equivalent to the size of an apple on the Moon seen from Earth. By combining high-frequency radio telescopes around the world, in a technique called very long baseline interferometry (VLBI), even such a tiny feature is, in principle, detectable.

In addition, the group wants to use the same radio telescopes to find and measure pulsars around the very same black hole. Pulsars are rapidly spinning neutron stars, which can be used as highly accurate natural clocks in space. While radio pulsars are found throughout the Milky Way, surprisingly none had been found in the center of the Milky Way until very recently.

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.

The National Radio Astronomy Observatory has released a new video about the Karl G. Jansky Very Large Array (VLA), narrated by actress Jodie Foster, for their Visitor Center near Socorro, New Mexico. (See Section 3.8d and Section 15.4.)

Credit: Wikipedia

Credit: Wikipedia

Called Beyond the Visible, the 24-minute movie tells the behind-the-scenes story of the operation and scientific achievements of the VLA, which has been at the forefront of astrophysical research since 1980. Spectacular ground and aerial footage of the iconic radio telescope is augmented by first-person interviews with staffers who keep the telescope working and scientists who use it to discover exciting new facts about the Universe. The documentary also depicts many of the technical tasks needed to keep the array functioning at the forefront of science.

Links: The NRAO has made the video available for viewing online here. An earlier movie “Into Deepest Space” tells the story of the Atacama Large Millimeter/submillimeter Array (ALMA).

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.