Author: Anne Minard

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Here at Universe Today, the subject of Newtonian gravity always seems to lead to vigorous debate. Now, there’s new research to stoke it.

Manuel Metz, and astrophysicist at the German Aero-space Center, and his colleagues say dwarf galaxies in the Milky Way are arranged in a way that precludes the existence of dark matter — but also depends on it. 

“Maybe Newton was indeed wrong,” said Pavel Kroupa, an astronomer at Bonn University. “Although his theory does, in fact, describe the everyday effects of gravity on Earth, things we can see and measure, it is conceivable that we have completely failed to comprehend the actual physics underlying the force of gravity.”

As modern cosmologists rely more and more on the ominous “dark matter” to explain otherwise inexplicable observations, much effort has gone into the detection of this mysterious substance in the last two decades, yet no direct proof could be found that it actually exists. Even if it does exist, dark matter would be unable to reconcile all the current discrepancies between actual measurements and predictions based on theoretical models. Hence the number of physicists questioning the existence of dark matter has been increasing for some time now. Competing theories of gravitation have already been developed which are independent of this construction. Their only problem is that they conflict with Newton’s theory of gravitation.

In two new studies, Metz and his team have examined so-called “satellite galaxies.” This term is used for dwarf galaxy companions of the Milky Way, some of which contain only a few thousand stars. According to the best cosmological models, they exist presumably in hundreds around most of the major galaxies. Up to now, however, only 30 such satellites have been observed around the Milky Way, a discrepancy in numbers which is commonly attributed to the fact that the light emitted from the majority of satellite galaxies is so faint they remain invisible.

A detailed study of these stellar agglomerates has revealed some astonishing phenomena: “First of all, there is something unusual about their distribution,” Kroupa said, “the satellites should be uniformly arranged around their mother galaxy, but this is not what we found.” More precisely, all classical satellites of the Milky Way – the eleven brightest dwarf galaxies – lie more or less in the same plane, they are forming some sort of a disc in the sky. The research team has also been able to show that most of these satellite galaxies rotate in the same direction around the Milky Way, like the planets revolve around the Sun.

The physicists believe that this phenomenon can only be explained if the satellites were created a long time ago through collisions between younger galaxies.

“The fragments produced by such an event can form rotating dwarf galaxies,” Metz said. But there is an interesting catch to this crash theory, “theoretical calculations tell us that the satellites created cannot contain any dark matter.” This assumption, however, stands in contradiction to another observation. “The stars in the satellites we have observed are moving much faster than predicted by the Gravitational Law. If classical physics holds this can only be attributed to the presence of dark matter.” 

Or one must assume that some basic fundamental principles of physics have hitherto been incorrectly understood. “The only solution would be to reject Newton’s classical theory of gravitation,” adds Kroupa. “We probably live in a non-Newton universe. If this is true, then our observations could be explained without dark matter.” Such approaches are finding support amongst other research teams in Europe, too.

It would not be the first time that Newton’s theory of gravitation had to be modified over the past hundred years. This became necessary in three special cases: when high velocities are involved (through the Special Theory of Relativity), in the proximity of large masses (through the theory of General Relativity), and on sub-atomic scales (through quantum mechanics). 

Source: Eurekalert. The relevant papers are available here and here.

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As the race ramps up to find Earth-like planets around other stars, lasers are a viable option.

That according to researchers at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, who have created an “astro-comb,” a sort of calibration tool based on wavelengths of light, to pick up minute variations in a star’s motion caused by orbiting planets.

In most cases, extrasolar planets can’t be seen directly—the glare of the nearby star is too great—but their influence can be discerned through spectroscopy, which analyzes the energy spectrum of the light coming from the star. Not only does spectroscopy reveal the identity of the atoms in the star (each element emits light at a certain characteristic frequency), it can also tell researchers how fast the star is moving away or toward Earth, courtesy of the Doppler effect, which occurs whenever a source of waves is itself in motion. By recording the change in the frequency of the waves coming from or bouncing off of an object, scientists can deduce the velocity of the object.

Though the planet might weigh millions of times less than the star, the star will be jerked around a tiny amount owing to the gravity interaction between star and planet. This jerking motion causes the star to move toward or away from Earth slightly in a way that depends on the planet’s mass and its nearness to the star. The better the spectroscopy used in this whole process, the better will be the identification of the planet in the first place and the better will be the determination of planetary properties.

Right now standard spectroscopy techniques can determine star movements to within a few meters per second. In tests, the Harvard researchers are now able to calculate star velocity shifts of less than 1 m (3.28 feet) per second, allowing them to more accurately pinpoint the planet’s location.

Smithsonian researcher David Phillips says that he and his colleagues expect to achieve even higher velocity resolution, which when applied to the activities of large telescopes presently under construction, would open new possibilities in astronomy and astro physics, including simpler detection of more Earth-like planets.

With this new approach, Harvard astronomers achieve their great improvement using a frequency comb as the basis for the astro-comb. A special laser system is used to emit light not at a single energy but a series of energies (or frequencies), evenly spaced across a wide range of values. A plot of these narrowly-confined energy components would look like the teeth of a comb, hence the name frequency comb. The energy of these comb-like laser pulses is known so well that they can be used to calibrate the energy of light coming in from the distant star. In effect, the frequency comb approach sharpens the spectroscopy process. The resultant astro-comb should enable a further expansion of extrasolar planetary detection.

The astro-comb method has been tried out on a medium-sized telescope in Arizona and will soon be installed on the much larger William Herschel Telescope, which resides on a mountaintop in the Canary Islands.

Preliminary results from the new technique were published in the April 3, 2008 issue of Nature. The Harvard group will present the most recent findings at the 2009 Conference on Lasers and Electro Optics/International Quantum Electronics Conference, May 31 to June 5 in Baltimore.

Source: Eurekalert

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This mysterious, giant object existed at a time when the universe was only about 800 million years old. It stretches for 55 thousand light years, a record for that early point in time. Its length is comparable to the radius of the Milky Way’s disk.

Besides being a great candidate for a future “Where in the Universe Challenge,” what is it?

In general, objects such as this one are dubbed extended Lyman-Alpha blobs; they are huge bodies of gas that may be precursors to galaxies.

And this blob was named Himiko for a legendary, mysterious Japanese queen.

Beyond that, researchers remain puzzled. It could be ionized gas powered by a super-massive black hole; a primordial galaxy with large gas accretion; a collision of two large young galaxies; super wind from intensive star formation; or a single giant galaxy with a large mass of about 40 billion Suns. Because this mysterious and remarkable object was discovered early in the history of the universe in a Japanese Subaru field, the researchers named the object after the legendary, mysterious queen.

“The farther out we look into space, the farther we go back in time, ” explained lead author Masami Ouchi, a fellow at the Observatories of the Carnegie Institution who led an international team of astronomers from the United States, Japan and the United Kingdom. “I am very surprised by this discovery. I have never imagined that such a large object could exist at this early stage of the universe’s history.”

Ouchi adds that, according to Big Bang cosmology, small objects form first and then merge to produce larger systems. “This blob had a size of typical present-day galaxies when the age of the universe was about 800 million years old, only 6 percent of the age of today’s universe,” he said.

Extended blobs discovered before now have mostly been seen at a distance when the universe was 2 to 3 billion years old. No extended blobs have previously been found when the universe was younger. Himiko is located at a transition point in the evolution of the universe called the reionization epoch—it’s as far back as we can see to date. And at 55 thousand light years, Himiko is a big blob for that time.

This reionizing chapter in the universe was at the cosmic dawn, the epoch between about 200 million and one billion years after the Big Bang. During this period, neutral hydrogen began to form quasars, stars, and the first galaxies. Astronomers probe this era by searching for characteristic hydrogen signatures from the scattering of photons created by ionized gas clouds.

The team initially identified Himiko among 207 distant galaxy candidates seen at optical wavelengths using the Subaru telescope from the Subaru/XMM-Newton Deep Survey Field located in the constellation of Cetus. They then made spectroscopic observations to measure the distance with the Keck/DEIMOS and Carnegie’s Magellan/IMACS instrumentation.

Himiko was an extraordinarily bright and large candidate for a distant galaxy.

“We hesitated to spend our precious telescope time by taking spectra of this weird candidate. We never believed that this bright and large source was a real distant object. We thought it was a foreground interloper contaminating our galaxy sample,” said Ouchi. “But we tried anyway. Then, the spectra exhibited a characteristic hydrogen signature clearly indicating a remarkably large distance—12.9 billion light years!”

Using infrared data from NASA’s Spitzer Space Telescope and the United Kingdom Infrared Telescope, radio data from the VLA, and X-ray imaging from the XMM-Newton satellite, Ouchi and his colleagues have been able to estimate the star-formation rate and stellar mass of the galaxy and to search for an active nucleus powered by a super-massive black hole.

“We found that the stellar mass of Himiko is an order of magnitude larger than other objects known at a similar epoch, but we cannot as yet tell if the center houses an active and growing black hole,” said James Dunlop, a team member from the University of Edinburgh. 

Alan Dressler, a team member from the Carnegie Institution, said it’s possible that Himiko is a member of a whole class of objects yet to be discovered.

“Because this object is, to this point, one-of-a-kind, it makes it very hard to fit it into the prevailing model of how normal galaxies were assembled. On the other hand, that’s what makes it interesting,” he said.

Source: Carnegie Institution. The research appears in the May 10, 2009, issue of The Astrophysical Journal (here).