Dwarf Galaxy Kiso 5639

A NEW APPROACH FOR DETECTING PLANETS IN THE ALPHA CENTAURI SYSTEM

Yale astronomers have taken a fresh look at the nearby Alpha Centauri star system and found new ways to narrow the search for habitable planets there.

According to a study led by Professor Debra Fischer and graduate student Lily Zhao, there may be small, Earth-like planets in Alpha Centauri that have been overlooked. Meanwhile, the study ruled out the existence of a number of larger planets in the system that had popped up in previous models.

“The universe has told us the most common types of planets are small planets, and our study shows these are exactly the ones that are most likely to be orbiting Alpha Centauri A and B,” said Fischer, a leading expert on exoplanets who has devoted decades of research to the search for an Earth analog.

The new study appears in the Astronomical Journal. Co-authors are John Brewer and Matt Giguere of Yale and Bárbara Rojas-Ayala of Universidad Andrés Bello in Chile.

The Alpha Centauri system is located 1.3 parsecs (24.9 trillion miles) from Earth, making it our closest neighboring system. It has three stars: Centauri A, Centauri B, and Proxima Centauri. Last year, the discovery of an Earth-like planet orbiting Proxima Centauri set off a new wave of scientific and public interest in the system.

“Because Alpha Centauri is so close, it is our first stop outside our solar system,” Fischer said. “There’s almost certain to be small, rocky planets around Alpha Centauri A and B.”

The findings are based on data coming in from a new wave of more advanced spectrographic instruments at observatories located in Chile: CHIRON, a spectrograph built by Fischer’s team; HARPS, built by a team from Geneva; and UVES, part of the Very Large Telescope Array. “The precision of our instruments hasn’t been good enough, until now,” Fischer said.

The researchers set up a grid system for the Alpha Centauri system and asked, based on the spectrographic analysis, “If there was a small, rocky planet in the habitable zone, would we have been able to detect it?” Often, the answer came back: “No.”

Zhao, the study’s first author, determined that for Alpha Centauri A, there might still be orbiting planets that are smaller than 50 Earth masses. For Alpha Centauri B there might be orbiting planets than are smaller than 8 Earth masses; for Proxima Centauri, there might be orbiting planets that are less than one-half of Earth’s mass.

In addition, the study eliminated the possibility of a number of larger planets. Zhao said this takes away the possibility of Jupiter-sized planets causing asteroids that might hit or change the orbits of smaller, Earth-like planets.

“This is a very green study in that it recycles existing data to draw new conclusions,” said Zhao. “By using the data in a different way, we are able to rule out large planets that could endanger small, habitable worlds and narrow down the search area for future investigations.”

This new information will help astronomers prioritize their efforts to detect additional planets in the system, the researchers said. Likewise, the continuing effort by Fischer and others to improve spectrographic technology will help identify and understand the composition of exoplanets.

Illustration by Michael S. Helfenbein

Omega Centauri (ω Cen), or NGC 5139; globular cluster in the constellation of Centaurus.

Right now Chandra is studying a galaxy in Ursa Major. Nearby in this dwarf galaxy, stars are forming at a furious rate! The galaxy, known as I Zwicky 18, is located about 59 million light years from Earth.

The constellation name, Ursa Major, means Big Bear. The “bear” association has its origins in two major civilizations which saw two very different bears in the sky. The Greeks who named this constellation (later translated into the Latin name we use today) thought that the stars outlined the shape of a bear walking about on its clawed feet. It and its smaller companion, Ursa Minor were said to be the prey of Boötes and his hunting dogs. The long cat-like tail on the bears was part of the ancient pattern and is somewhat of a mystery. A story in Ovid tried to offer an explanation. In that myth, Zeus fell in love with Callisto. Hera changed her into a bear out of jealousy. Her son Arcus (the namesake of Arcturus, the alternate name for the constellation Boötes) came upon her in the forest and she ran to greet him. Not knowing the bear was his mother, he was about to kill her. To save her, Zeus turned Arcus into a smaller bear, grabbed them both by their tails and flung them into the sky, causing their tails to be stretched. A number of Native American tribes also referred to this constellation as a bear, but with a clever addition. In their description of these stars, the bear is the same, but without the “tail”. Instead, those three stars are three hopeful hunters, and the middle one is carrying a cooking pot for cooking up the bear. Johannes Hevelius’ Ursa Major from Uranographia (1690) The most common pattern seen in this constellation is composed of a smaller group of the brightest stars (called an asterism) that outline the Big Dipper. This name comes from many different cultures which have seen in these stars a long handled spoon, often used for dipping water for drinking. Others call this pattern a plow, seeing instead of a dipper, an old-style, ox-pulled farm plow. The plow pattern, pulled by oxen, is the shape referenced in the myth of the Triones, the oxen and plow driven by Bootes the herder. The Egyptians and the Chinese saw different associations. Even in relatively more modern times, early European civilizations continued to invent new meanings for this pattern.

Constellation map from: http://www.lunarplanner.com/StarsProperMotion/UrsaMajor/

For a list of objects in Ursa Major that Chandra has observed and article, see link:  http://chandra.si.edu/photo/constellations/ursamajor.html

Hubble Mosaic of the Majestic Sombrero Galaxy

credit: Patrice Paquette

EBLM J0555-57Ab is the smallest star ever known

Ribbons and pearls -the barred spiral galaxy NGC 1398 [3416 x 3463]

HH34 - Subaru Data + colors from DSS (2) Credit: Roberto colombari

“Cosmic Neutrinos Can be Absorbed by Planet Earth”

 Scientists using the IceCube Observatory located near the South Pole have discovered that neutrinos can be absorbed by our Planet Earth. With almost no mass and no charge, these particles rarely interact with matter. Yet tens of trillions of neutrinos pass through our bodies every second.  Previous theories predicted that at high energies, neutrinos can be expected to interact with matter and be absorbed by the Earth instead of passing through the planet.  “We knew that lower-energy neutrinos pass through just about anything, but although we had expected higher-energy neutrinos to be different, no previous experiments had been able to demonstrate convincingly that higher-energy neutrinos could be stopped by anything,” said Penn State Professor Doug Cowen. “However, the neutrino does have a tiny probability to interact, and this probability increases with energy. That probability is what scientists call the neutrino cross section.”  The new measurements recorded by IceCube determined the neutrino cross section energies to be about 6.3 TeV and 980 TeV, energy levels significantly higher than previously measured.

Read more about this fascinating story at: http://www.newsoftheuniverse.com/2017/11/cosmic-neutrinos-can-be-absorbed-by.html