Future Tech: Lasers Explore Early Galaxies and Milky Way’s Supermassive Black Hole




It’s not the sequel to War of the Worlds! Astronomers at the Very Large Telescope (VLT) site in Chile are trying to measure the distortions of Earth’s ever changing atmosphere. Constant imaging of high-altitude atoms excited by the laser — which appear like an artificial star — allow astronomers to instantly measure atmospheric blurring.  In this case, the VLT was observing our Galaxy’s center, and so Earth’s atmospheric blurring in that direction was needed.



At the center of the Milky Way is Sagittarius A -believed to be a supermassive black hole, which lurk at the center of all known spiral galaxies. If we can observe Sagittarius A*’s surroundings we can confirm once and for all whether it’s a black hole – and prove Einstein right (or wrong!) . Relativity theory predicts the existence of black holes. If relativity breaks down, we might not see a black hole at all, but something totally weird.

Relativity describes how large masses can bend space, and a black hole is where the mass is so large that space gives up altogether and becomes a singularity.  Black holes are already well understood, we think, but we’ve only ever observed them at second hand – the behavior of orbiting objects or bent light rays.  To actually view the shadow of a black hole, the cut-off point where light is swallowed and cannot escape, would be a massive advance – and only the beginning.

Detailed observation of the area around the Sag A* border would be a goldmine of information. The spin and rate of matter inflow into the central black hole will tell us about the Milky Way’s creation, as well as providing further extreme tests of general relativity.  We could even see frame dragging, which sounds like a video game hardware issue but is actually something that could happen to reality – where a spinning black hole grabs hold of space and literally pulls reality around after it.

The rock star at center of Earth’s microwave eye will be in the high deserts of Chile, where the Atacama 66-dish Large Millimeter/Submillimeter Array (ALMA) is being built, which should be up and running by 2012. In concert with other scopes across the planet. ALMA will should provide a much clearer picture of Sag A*

ALMA is a giant, international observatory composed initially of 66 high-precision telescopes, operating at wavelengths of 0.3 to 9.6 mm. The ALMA antennas will be electronically combined and provide astronomical observations which are equivalent to a single large telescope of tremendous size and resolution, able to probe the Universe at millimeter and sub-millimeter wavelengths with unprecedented sensitivity and resolution, with an accuracy up to ten times better than the Hubble Space Telescope.

Meanwhile astronomers are using the W. M. Keck Observatory laser to probe the nature of massive galaxies in the early universe. The Keck laser team have discovered distant galaxies as massive as the Milky Way yet ten to 1000 times more compact. The new results, announced June 9 at the 214th American Astronomical Society meeting in Pasadena, provide astronomers with surprising clues about early star and galaxy formation at a time when the Universe was just a few billion years old.

“The shapes of these galaxies tell us that it is not reasonable to expect they could occur from mergers. Instead, the kind of disks we’re seeing and the constituent stars seemed to have formed all at once, directly from the gas. In the old lingo, this is monolithic galaxy formation,” said astronomer Alan Stockton of the University of Hawai’i.

He and his colleagues Dr. Gabriela Canalizo of the University of California, Riverside and Dr. Elizabeth McGrath of the University of California, Santa Cruz used the Keck II telescope and its Laser Guide Star Adaptive Optics, or LGSAO, to image radio galaxies and quasars that are roughly 11 billion light years from Earth.

The Keck LGSAO system uses a powerful laser to excite sodium atoms in the upper atmosphere so that they emit light and appear as an artificial star. Astronomers use this artificial starlight to analyze how the atmosphere is distorting incoming light from their target astronomical sources. The distortion can then be corrected using a compensating distortion in a deformable mirror in the adaptive optics system.

From these AO-corrected observations of distant galaxies, Stockton and his colleagues could model the detailed structures of their target galaxies, which are quite unlike those of massive galaxies in the present-day Universe. The team found the objects had masses that were a hundred billion times the mass of the Sun, yet were compact and have diameters of roughly 3,000 to 15,000 light years. By comparison, the diameter of the Milky Way is 100,000 light years, yet it has a mass of about 500 billion solar masses.

Teams using the Hubble Space Telescope have also found that high redshift galaxies tend to be more compact than astronomers expected. Stockton said his team was able to obtain near-infrared images from the ground that were almost two times sharper than those they could obtain with the Hubble Space Telescope at similar wavelengths. These Keck LGSAO images allow not only the measurement of characteristic sizes of the distant galaxies, but also more detailed properties of the light distribution that may give clues to formation processes.

For example, Stockton’s team imaged a field of five galaxies two of which show a tidal tail (Fig. 2) that would be indistinguishable with Hubble. “The tail, however, can only form if the galaxies we observe were disk galaxies,” Stockton said. “This Keck data gives us further evidence of that conclusion.”

Astronomers expected that distant galaxies might be disk galaxies and would be more compact than today’s galaxies. They did not expect the galaxies to be as dense as Stockton’s observations indicate, and researchers have not yet identified objects in the local Universe that resemble these compact disk galaxies. This is surprising because dense, disk-like objects are like cannon balls and are therefore not easily destroyed by collisions, meaning some should survive today.

“It might therefore be possible that these disk galaxies have instead become the cores of today’s galaxies,” Stockton said.

The data cannot yet answer this or other questions about the morphology and evolution of these two billion-year-old galaxies. Stockton said that he is currently trying to obtain clearer spectral data of the distant galaxies to determine how fast their constituent stars are moving about their centers—this will enable astronomers to independently determine the galaxies’ masses. His team
is also currently looking for examples of very compact galaxies that have survived to a time when the Universe was half its present age, about seven billion years old. It will be possible to obtain much more detailed observations of such galaxies, which may lead to a better physical understanding of these objects. Observations to find disk galaxies at more distant redshifts will also be done to determine if disk galaxies exist in the very early Universe, Stockton said.

The Keck II telescope and its LGSAO are operated by the W. M. Keck Observatory, which manages twin ten-meter optical/infrared telescopes on the summit of Mauna Kea on the island of Hawai’i. The two telescopes feature a suite of advanced instrumentation including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrographs and a world-leading laser-guide-star adaptive optics system.

Casey Kazan with Luke McKinney

Image Credit: Yuri Beletsky (ESO)
Source: APOD


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