AC4C. Stay Current—Fathoming Huge Distances
Staying current for Chapter 4
Articles from 2009–present
2016-12-30. Astronomer Edwin Hubble announced the discovery of other galaxies beyond the Milky Way on this date in 1924. By Writer’s Almanac. Excerpt: …Before he made his discovery, everyone thought that our Milky Way galaxy was the only galaxy in the universe, and that there wasn’t much outside it besides the Magellanic Clouds, which are visible by the naked eye in the Southern Hemisphere, and which were thought to be clouds of gas or dust. …Hubble first published his discovery in a paper called “Extragalactic Nature of Spiral Nebulae,” which was presented on this date, in his absence, at a joint meeting of the American Astronomical Society and the American Association for the Advancement of Science. …Hubble had written his doctoral dissertation on “Photographic Investigations of Faint Nebulae.” With older or smaller telescopes, nebulae just looked like clouds of glowing gas, but with the Hooker telescope — the most powerful telescope in the world at that time — Hubble was able to see that there were actually stars within the nebula. One of the stars in the Andromeda Nebula turned out to be a Cepheid variable: a particular type of star that pulsates and is very bright. A Harvard computationist named Henrietta Leavitt had figured out a decade earlier that, by observing a Cepheid variable and measuring its brightness and the length of time it takes to go from bright to dim and back again, they could calculate the star’s distance from the Earth. Hubble did the math and realized, to his amazement, that the star he was observing — which he called V1, or “variable number 1” — was almost 900,000 light years away. That’s more than eight times the distance of the farthest star in the Milky Way. It was then that he realized that the cloud of gas he’d been observing was really another vast galaxy that was very far away. He renamed the Andromeda Nebula the “Andromeda galaxy,” and he went on to discover 23 more separate galaxies. Within a few years of Hubble’s discovery, most astronomers came to agree that our galaxy is just one of millions. Methods to measure astronomical distance have gotten more precise, and it’s now estimated that the Andromeda galaxy is 2 million light years from Earth…. http://writersalmanac.org/episodes/20161230/
2016-06-02. Universe expanding faster than expected. By Robert Sanders, UC Berkeley News. Excerpt: Astronomers have obtained the most precise measurement yet of how fast the universe is expanding, and it doesn’t agree with predictions based on other data and our current understanding of the physics of the cosmos. The discrepancy — the universe is now expanding 9 percent faster than expected — means either that measurements of the cosmic microwave background radiation are wrong, or that some unknown physical phenomenon is speeding up the expansion of space, the astronomers say. …By measuring about 2,400 Cepheid stars in 19 nearby galaxies and comparing the apparent brightness of both types of stars, the researchers accurately determined the true brightness of the Type Ia supernovae. They then used this calibration to calculate distances to roughly 300 Type Ia supernovae in far-flung galaxies. “We needed both the nearby Cepheid distances for galaxies hosting Type Ia supernovae and the distances to the 300 more-distant Type Ia supernovae to determine the Hubble constant,” Filippenko said. “The paper focuses on the 19 galaxies and getting their distances really, really well, with small uncertainties, and thoroughly understanding those uncertainties.”… http://news.berkeley.edu/2016/06/02/universe-expanding-faster-than-expected/ 0
2014-04-10. NASA’s Hubble Extends Stellar Tape Measure 10 Times Farther Into Space. Excerpt: …astronomers now can precisely measure the distance of stars up to 10,000 light-years away — 10 times farther than previously possible…employing a technique called spatial scanning, which dramatically improves Hubble’s accuracy for making angular measurements. The technique, when applied to the age-old method for gauging distances called astronomical parallax, extends Hubble’s tape measure 10 times farther into space. …Parallax, a trigonometric technique, is the most reliable method for making astronomical distance measurements, and a practice long employed by land surveyors here on Earth. The diameter of Earth’s orbit is the base of a triangle and the star is the apex where the triangle’s sides meet. The lengths of the sides are calculated by accurately measuring the three angles of the resulting triangle. …This new long-range precision was proven when scientists successfully used Hubble to measure the distance of a special class of bright stars called Cepheid variables, approximately 7,500 light-years away in the northern constellation Auriga. The technique worked so well, they are now using Hubble to measure the distances of other far-flung Cepheids. Such measurements will be used to provide firmer footing for the so-called cosmic “distance ladder.” This ladder’s “bottom rung” is built on measurements to Cepheid variable stars that, because of their known brightness, have been used for more than a century to gauge the size of the observable universe. They are the first step in calibrating far more distant extra-galactic milepost markers such as Type Ia supernovae. …To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when Earth was on opposite sides of the sun. A very subtle shift in the star’s position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble’s Wide Field Camera 3, which has 16.8 megapixels total. A third exposure was taken after another six months to allow for the team to subtract the effects of the subtle space motion of stars, with additional exposures used to remove other sources of error. …visit: http://www.nasa.gov/hubble… http://www.nasa.gov/press/2014/april/nasas-hubble-extends-stellar-tape-measure-10-times-farther-into-space/#.U0cDuMdGLHQ. By NASA RELEASE 14-104.
2014-01-08. Universe Measured to One-Percent Accuracy: Most Precise Calibration Yet of Cosmic ‘Standard Ruler’. Excerpt: Today the Baryon Oscillation Spectroscopic Survey (BOSS) Collaboration announced that BOSS has measured the scale of the universe to an accuracy of one percent. This and future measures at this precision are the key to determining the nature of dark energy.
…Baryon acoustic oscillations (BAO) are the regular clustering of galaxies, whose scale provides a “standard ruler” to measure the evolution of the universe’s structure. Accurate measurement dramatically sharpens our knowledge of fundamental cosmological properties, including how dark energy accelerates the expansion of the universe.
Combined with recent measures of the cosmic microwave background radiation (CMB) and supernova measures of accelerating expansion, the BOSS results suggest that dark energy is a cosmological constant whose strength does not vary in space or time. Although unlikely to be a flaw in Einstein’s General Theory of Relativity, the authors of the BOSS analysis note that “understanding the physical cause of the accelerated expansion remains one of the most interesting problems in modern physics.”
Among other cosmic parameters, says White, the BOSS analysis “also provides one of the best-ever determinations of the curvature of space. The answer is, it’s not curved much.”
Calling a three-dimensional universe “flat” means its shape is well described by the Euclidean geometry familiar from high school: straight lines are parallel and triangles add up to 180 degrees. Extraordinary flatness means the universe experienced relatively prolonged inflation, up to a decillionth of a second or more, immediately after the big bang.
“One of the reasons we care is that a flat universe has implications for whether the universe is infinite,” says Schlegel. “That means – while we can’t say with certainty that it will never come to an end – it’s likely the universe extends forever in space and will go on forever in time. Our results are consistent with an infinite universe.” … http://newscenter.lbl.gov/news-releases/2014/01/08/boss-one-percent/ DOE/LBNL
2012-10-03. NASA’s Infrared Observatory Measures Expansion of Universe | NASA RELEASE : 12-343. Relevant to GSS A Changing Cosmos chapter 4. Excerpt: …Astronomers using NASA’s Spitzer Space Telescope have announced the most precise measurement yet of the Hubble constant, or the rate at which our universe is stretching apart. …It improves by a factor of 3 on a similar, seminal study from the Hubble telescope and brings the uncertainty down to 3 percent, a giant leap in accuracy for cosmological measurements. The newly refined value for the Hubble constant is 74.3 ± 2.1 kilometers per second per megaparsec. A megaparsec is roughly 3 million light-years. …Glenn Wahlgren, Spitzer program scientist … said infrared vision, which sees through dust to provide better views of variable stars called cepheids, enabled Spitzer to improve on past measurements of the Hubble constant. … Cepheids are crucial to the calculations because their distances from Earth can be measured readily. In 1908, Henrietta Leavitt discovered these stars pulse at a rate directly related to their intrinsic brightness. …By measuring how bright they appear on the sky, and comparing this to their known brightness as if they were close up, astronomers can calculate their distance from Earth.
Spitzer observed 10 cepheids in our own Milky Way galaxy and 80 in a nearby neighboring galaxy called the Large Magellanic Cloud. … “Just over a decade ago, using the words ‘precision’ and ‘cosmology’ in the same sentence was not possible, and the size and age of the universe was not known to better than a factor of two,” said Freedman. “Now we are talking about accuracies of a few percent.” … Read the full article: http://www.nasa.gov/home/hqnews/2012/oct/HQ_12-343_Spitzer_Cepheid.html
2011 Jan 12. Cosmology Standard Candle Not So Standard After All. NASA Spitzer Project. Excerpt: PASADENA, Calif. — Astronomers have turned up the first direct proof that “standard candles” used to illuminate the size of the universe, termed Cepheids, shrink in mass, making them not quite as standard as once thought. The findings, made with NASA’s Spitzer Space Telescope, will help astronomers make even more precise measurements of the size, age and expansion rate of our universe.
2009 October 22. Galaxy cluster smashes distance record. EurekAlert. Excerpt: The most distant galaxy cluster yet has been discovered by combining data from NASA’s Chandra X-ray Observatory and optical and infrared telescopes. The cluster is located about 10.2 billion light years away, and is observed as it was when the Universe was only about a quarter of its present age.
The galaxy cluster, known as JKCS041, beats the previous record holder by about a billion light years. Galaxy clusters are the largest gravitationally bound objects in the Universe. Finding such a large structure at this very early epoch can reveal important information about how the Universe evolved at this crucial stage.
JKCS041 is found at the cusp of when scientists think galaxy clusters can exist in the early Universe based on how long it should take for them to assemble. Therefore, studying its characteristics – such as composition, mass, and temperature – will reveal more about how the Universe took shape.
“This object is close to the distance limit expected for a galaxy cluster,” said Stefano Andreon of the National Institute for Astrophysics (INAF) in Milan, Italy. “We don’t think gravity can work fast enough to make galaxy clusters much earlier.”…
2009 October 19. Up the Cosmic Distance Ladder. By Lee Billings, Seed Magazine. Excerpt: The development of astronomy can be seen as a millenia-long quest to measure and know the true scale of the natural world.
One of the greatest difficulties when discussing the physical world is conveying its immense scale. While we can estimate the number of molecules contained in a single drop of water (roughly 1.5 sextillion, 1,500,000,000,000,000,000,000) or measure the distance light traverses in a single second (around 300 million meters), the values we obtain are so alien that we cannot intuitively comprehend them. For most people, the difference between one and 10 is far more palpable than the difference between a thousand billion and a thousand trillion…. Few disciplines illustrate this more clearly than astronomy, the oldest of the natural sciences.
…Just how is it that we know the distance from the Earth to the Sun, the other planets, and faraway stars? How do we know the architecture and future of our galaxy or the expansion rate of the universe? The short answer is that we know these things because of the cosmic distance ladder, a suite of interdependent methods to measure successively greater distances in the universe. Though most of the ladder was created in the 20th century, millennia of effort have contributed to its construction, and it is still being refined….
2009 April 28. Most distant object in the universe spotted. By Rachel Courtland, NewScientist. Excerpt: Astronomers have spotted the most distant object yet confirmed in the universe – a self-destructing star that exploded 13.1 billion light years from Earth. It detonated just 640 million years after the big bang, around the end of the cosmic “dark ages”, when the first stars and galaxies were lighting up space.
The object is a gamma-ray burst (GRB) – the brightest type of stellar explosion. GRBs occur when massive, spinning stars collapse to form black holes and spew out jets of gas at nearly the speed of light. These jets send gamma rays our way, along with “afterglows” at other wavelengths, which are produced when the jet heats up surrounding gas.
…Some of the first observations were made on Mauna Kea in Hawaii with the United Kingdom Infrared Telescope and the Gemini North telescope.
Other telescopes later measured the spectrum of the afterglow, revealing that the burst detonated about 13.1 billion light years from Earth. “It’s the most distant gamma-ray burst, but it’s also the most distant object in the universe overall,” says Edo Berger of the Harvard-Smithsonian Center for Astrophysics, a member of the team that observed the afterglow with Gemini North.
To gauge an object’s distance, astronomers measure how much an object’s light has been stretched, or reddened, by the expansion of space. This burst lies at a redshift of 8.2, more distant than the previous GRB record holder, which lay at a redshift of 6.7….
…For astronomy, this is a watershed event,” Joshua Bloom of the University of California, Berkeley, who observed the afterglow using the Gemini South telescope in Chile, told New Scientist.”This is the beginning of the study of the universe as it was before most of the structure that we know about today came into being.”….