Hubble surveys galaxy clusters, looks for dark matter effects

Photo: Hubble Space Telescope image of galaxy cluster MACS J1206.2-0847
Hubble Space Telescope image of galaxy cluster MACS J1206.2-0847. Credit: NASA, ESA, M. Postman (STScI) and the CLASH Survey Team

October 13 — The NASA/ESA Hubble Space Telescope has been used to make an image of galaxy cluster MACS J1206.2-0847. The apparently distorted shapes of distant galaxies in the background is caused by an invisible substance called dark matter, whose gravity bends and distorts their light rays. MACS 1206 has been observed as part of a new survey of galaxy clusters using Hubble.

Cluster MACS J1206.2-0847 (or MACS 1206 for short) is one of the first targets in a Hubble survey that will allow astronomers to construct the highly detailed dark matter maps of more galaxy clusters than ever before. These maps are being used to test previous but surprising results that suggest that dark matter is more densely packed inside clusters than some models predict. This might mean that galaxy cluster assembly began earlier than commonly thought.

The Cluster Lensing And Supernova survey with Hubble (CLASH) probes, with unparalleled precision, the distribution of dark matter in 25 massive clusters of galaxies. So far, the CLASH team has observed six of the 25 clusters.

Dark matter makes up the bulk of the Universe’s mass, yet it can only be detected by measuring how its gravity tugs on visible matter and warps the fabric of space-time like a fairground mirror so that the light from distant objects is distorted.

Galaxy clusters like MACS 1206 are perfect laboratories for studying dark matter’s gravitational effects because they are the most massive structures in the Universe to be held together by gravity. Because of their immense gravitational pull, the clusters act like giant cosmic lenses, amplifying, distorting and bending any light that passes through them — an effect known as gravitational lensing.

Lensing effects can also produce multiple images of the same distant object, as is evident in this Hubble picture. In particular, the apparent numbers and shapes of the distant galaxies far beyond a galaxy cluster become distorted as the light passes through, yielding a visible measurement of how much mass there is in the intervening cluster, and how it is distributed. The substantial lensing distortions seen are proof that the dominant mass component of the clusters is dark matter. The distortions would be far weaker if the clusters’ gravity came only from visible matter.

MACS 1206 lies four billion light-years from Earth. Hubble’s keen vision helped CLASH  astronomers to uncover 47 multiple images of 12 newly identified faraway galaxies. Finding  so many multiple images in a cluster is a unique capability of Hubble, and the CLASH survey  is optimised to find them. The new observations build on earlier work by Hubble and  ground-based telescopes.

Among the observations which complement Hubble’s is a major project using the  European Southern Observatory’s Very Large Telescope. Unlike Hubble, which is making  images of the clusters, the VLT is carrying out spectroscopic observations, where  instruments split up the galaxies’ light into their component colours letting the scientists  draw inferences about many of the properties of the cluster galaxies, including their  distance and chemical makeup.

Taking advantage of two of Hubble’s powerful cameras, the Advanced Camera for Surveys  and the Wide Field Camera 3, the CLASH survey covers a broad wavelength range, from  ultraviolet to near-infrared.

Astronomers need the diverse colors to estimate the distances to the lensed galaxies  and to study them in more detail. Hubble’s unique capabilities allow astronomers to  estimate distances to galaxies that are four times fainter than those that ground-based  telescopes can see.

The era when the first clusters formed is not precisely known, but is estimated to be at  least nine billion years ago and possibly as far back as twelve billion years ago. If most of  the clusters in the CLASH survey are found to have excessively high accumulations of dark  matter in their central cores, then it may yield new clues about the early stages of the  origin of structure in the Universe.

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A summer gem

by Bill Murmann

Image: Star chart showing constellation Cygnus.
Constellation Cygnus with Albireo circled at the Swan's head. Image via Stellarium by James Guilford.

During the summer, one of the best colorful double stars is Albireo, the head of the “Swan” in the constellation Cygnus. “Double Stars” was the topic for the program at our monthly meeting on Monday, September 12, and Albireo is a great example. Albireo is 380 light years away; the pair of stars is designated “Albireo A” and “Albireo B.”

Albireo A is yellow star, slightly cooler than our Sun. It has a surface temperature estimated at 7,000 degrees F., compared to the Sun’s 9,000-degree F. surface temperature.

Its companion, Albireo B, is a hot, blue star with an estimated surface temperature of about 23,000 degrees F. It also rotates very fast — at about 560,000 MPH.

When we are looking at Albireo, we are actually seeing three stars. Albireo A is, itself, a close binary star. Most of us, however, can’t split this pair with our telescopes. It takes a minimum 20-inch telescope under really good sky conditions to split Albireo A. Paul Leopold with his 20-inch scope is probably the only CAA member who has a chance to see all three stars in Albireo.

Observatory Park is dedicated

The Geauga Park District’s new Observatory Park was dedicated on Saturday, August 20, with a program from 4 PM to midnight.

CAA members Bill Murmann, Bob Wiersma, and Susan Petsche attended the event, which also marked the 50th Anniversary celebration for the Geauga Park District.

Observatory Park, located in Geauga County’s Montville Township, features the new Oberle Observatory with a 25-inch telescope. The observatory was officially opened with a ribbon-cutting at 9:15 PM.

Stargazing until midnight was supposed to be part of the program after the ribbon-cutting. Unfortunately, the skies were cloudy. As the ribbon-cutting took place, however, the skies briefly cleared just enough to show Arcturus, Vega, and part of the handle of the Big Dipper.

Our neighbors and fellow amateur astronomers in the Chagrin Valley Astronomical Association (CVAS) played a key role in establishing the Oberle Observatory, and will continue to assist the Park District in its operation. The 1,100-acre Observatory Park has been designated an official dark-sky site by the International Dark-Sky Association (IDA).

Eventually, the site will also include the Nassau Station Observatory with its 36-inch research telescope that was formerly operated by the astronomy department at Case Western Reserve University.

Findley State Park star party Saturday, September 3

CAA will host a star party on the beach at Findley State Park from 9 PM to midnight (or so) on Saturday, September 3, weather permitting. The Findley program was originally set for August 6. It had to be rescheduled due to bad weather. This is the last Saturday date with a favorable Moon available for the year because park nature programs close down after the Labor Day weekend.

Those who have experienced it say that this is a great dark-sky site. Park Naturalist Roger Nikiforow said we could expect between 100 and 200 people for the program. The concession stand will be kept open before and during our star party. Nikiforow will be giving a presentation about astronomy from 7-8 PM in the nature center, and will join us with his telescope around 8:30 PM.

Any club members who would like to join us for the star party are welcome to bring a scope and come on out, though all complimentary camping sites for volunteers have been taken.

Everyone’s invited!

Findley State Park, Wellington, Ohio

Comet Elenin poses no threat to Earth

Often, comets are portrayed as harbingers of gloom and doom in movies and on television, but most pose no threat to Earth. Comet Elenin, the latest comet to visit our inner solar system, is no exception. Elenin will pass about 22 million miles (35 million kilometers) from Earth during its closest approach on Oct. 16, 2011.

Also known by its astronomical name C/2010 X1, the comet was first detected on Dec. 10, 2010 by Leonid Elenin, an observer in Lyubertsy, Russia, who made the discovery “remotely” using an observatory in New Mexico. At that time, Elenin was about 401 million miles (647 million kilometers) from Earth. Since its discovery, Comet Elenin has – as all comets do – closed the distance to Earth’s vicinity as it makes its way closer to perihelion, its closest point to the sun.

Image: Diagram of the projected course of Comet Elenin
The projected path of Comet Elenin. Trajectory of comet Elenin. Image credit: NASA/JPL-Caltech

NASA scientists have taken time over the last several months to answer your questions. Compiled below are the some of the most popular questions, with answers from Don Yeomans of NASA’s Near-Earth Object Program Office at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and David Morrison of the NASA Astrobiology Institute at the NASA Ames Research Center in Moffett Field, Calif.

Most Popular Questions About Comet Elenin

Q: When will Comet Elenin come closest to the Earth and appear the brightest?

A: Comet Elenin should be at its brightest shortly before the time of its closest approach to Earth on Oct. 16, 2011. At its closest point, it will be 22 million miles (35 million kilometers) from us.

Q: Will Comet Elenin come close to the Earth or between the Earth and the moon?

A: Comet Elenin will not come closer to Earth than 22 million miles (35 million kilometers). That’s more than 90 times the distance to the moon.

Q: Can this comet influence us from where it is, or where it will be in the future? Can this celestial object cause shifting of the tides or even tectonic plates here on Earth?

A: There have been incorrect speculations on the Internet that alignments of comet Elenin with other celestial bodies could cause consequences for Earth and external forces could cause comet Elenin to come closer. “Any approximate alignments of comet Elenin with other celestial bodies are meaningless, and the comet will not encounter any dark bodies that could perturb its orbit, nor will it influence us in any way here on Earth,” said Don Yeomans, a scientist at NASA JPL.

“Comet Elenin will not only be far away, it is also on the small side for comets,” said Yeomans. “And comets are not the most densely-packed objects out there. They usually have the density of something akin to loosely packed icy dirt.

“So you’ve got a modest-sized icy dirtball that is getting no closer than 35 million kilometers (about 22 million miles),” said Yeomans. “It will have an immeasurably miniscule influence on our planet. By comparison, my subcompact automobile exerts a greater influence on the ocean’s tides than comet Elenin ever will.”

Q: I’ve heard about three days of darkness because of Comet Elenin. Will Elenin block out the sun for three days?

A: “As seen from the Earth, comet Elenin will not cross the sun’s face,” says Yeomans.

But even if it could cross the sun, which it can’t, astrobiologist David Morrison notes that comet Elenin is about 2-3 miles (3-5 kilometers) wide, while the sun is roughly 865,000 miles (1,392,082 kilometers) across. How could such a small object block the sun, which is such a large object?

Let’s think about an eclipse of the sun, which happens when the moon appears between the Earth and the sun. The moon is about 2,500 miles (4,000 kilometers) in diameter, and has the same apparent size as the sun when it is about 250,000 miles (400,000 kilometers) away — roughly 100 times its own diameter. For a comet with a diameter of about 2-3 miles (3-5 kilometers) to cover the sun it would have to be within 250 miles (400 kilometers), roughly the orbital altitude of the International Space Station. However, as stated above, this comet will come no closer to Earth than 22 million miles.

Q: I’ve heard there is a “brown dwarf” theory about Comet Elenin. Would its mass be enough to pull Comet Honda’s trajectory a significant amount? Could this be used to determine the mass of Elenin?

A: Morrison says that there is no ‘brown dwarf theory’ of this comet. “A comet is nothing like a brown dwarf. You are correct that the way astronomers measure the mass of one object is by its gravitational effect on another, but comets are far too small to have a measureable influence on anything.”

Q: If we had a black or brown dwarf in our outer solar system, I guess no one could see it, right?

A: “No, that’s not correct,” says Morrison. “If we had a brown dwarf star in the outer solar system, we could see it, detect its infrared energy and measure its perturbing effect on other objects. There is no brown dwarf in the solar system, otherwise we would have detected it. And there is no such thing as a black dwarf.”

Q: Will Comet Elenin be visible to the naked eye when it’s closer to us? I missed Hale-Bopp’s passing, so I want to know if we’ll actually be able to see something in the sky when Elenin passes.

A: We don’t know yet if Comet Elenin will be visible to the naked eye. Morrison says, “At the rate it is going, seeing the comet at its best in early October will require binoculars and a very dark sky. Unfortunately, Elenin is no substitute for seeing comet Hale-Bopp, which was the brightest comet of the past several decades.”

“This comet may not put on a great show. Just as certainly, it will not cause any disruptions here on Earth. But, there is a cause to marvel,” said Yeomans. “This intrepid little traveler will offer astronomers a chance to study a relatively young comet that came here from well beyond our solar system’s planetary region. After a short while, it will be headed back out again, and we will not see or hear from Elenin for thousands of years. That’s pretty cool.”

Q: This comet has been called ‘wimpy’ by NASA scientists. Why?

A: “We’re talking about how a comet looks as it safely flies past us,” said Yeomans of NASA’s Near-Earth Object Program Office. “Some cometary visitors arriving from beyond the planetary region – like Hale-Bopp in 1997 — have really lit up the night sky where you can see them easily with the naked eye as they safely transit the inner-solar system. But Elenin is trending toward the other end of the spectrum. You’ll probably need a good pair of binoculars, clear skies and a dark, secluded location to see it even on its brightest night.”

Q: Why aren’t you talking more about Comet Elenin? If these things are small and nothing to worry about, why has there been no public info on Comet Elenin?

A: Comet Elenin hasn’t received much press precisely because it is small and faint. Several new comets are discovered each year, and you don’t normally hear about them either. The truth is that Elenin has received much more attention than it deserves due to a variety of Internet postings that are untrue. The information NASA has on Elenin is readily available on the Internet. (See http://www.jpl.nasa.gov/news/news.cfm?release=2011-135) If this comet were any danger to anyone, you would certainly know about it. For more information, visit NASA’s AsteroidWatch site at http://www.jpl.nasa.gov/asteroidwatch/.

Q: I’ve heard NASA has observed Elenin many times more than other comets. Is this true, and is NASA playing this comet down?

A: NASA regularly detects, tracks and characterizes asteroids and comets passing relatively close to Earth using both ground- and space-based telescopes. The Near-Earth Object Observations Program, commonly called “Spaceguard,” discovers these objects, characterizes a subset of them and predicts their paths to determine if any could be potentially hazardous to our planet. For more information, visit the NASA-JPL Near Earth objects site at http://neo.jpl.nasa.gov/ .

However, neither NASA nor JPL is in the business of actively observing Elenin or any other comet. Most of the posted observations are made by amateur astronomers around the world. Since Elenin has had so much publicity, it naturally has attracted more observers.

Q: I was looking at the orbital diagram of Comet Elenin on the JPL website, and I was wondering why the orbit shows some angles when zooming? If you pick any other comet, you can see that there are no angles or bends.

A: Many people are trying to plot the orbit of the comet with the routine on the JPL website, without realizing that this is just a simple visualization tool. While the tool has been recently improved to show smoother trajectories near the sun, it is not a scientific program to generate an accurate orbit. Yeomans explains that the orbit plotter on the Near-Earth Object website is not meant to accurately depict the true motion of objects over long time intervals, nor is it accurate during close planetary encounters. For more accurate long-term plotting, Yeomans suggests using the JPL Horizons system.

From a NASA Jet Propulsion Laboratory news release.

Oppy reaches Endeavour Crater

Photo: Edge of Endeavour Crater on planet Mars.
NASA's Mars Exploration Rover Opportunity arrived at the rim of Endeavour crater on Aug. 9, 2011, after a trek of more than 13 miles (21 kilometers) lasting nearly three years. Image Credit: NASA/JPL-Caltech/Cornell/ASU. (Click on image to see full-size.)

PASADENA, Calif. – After a journey of almost three years, NASA’s Mars Exploration Rover Opportunity has reached the Red Planet’s Endeavour Crater to study rocks never seen before.

On Aug. 9, the golf cart-sized rover relayed its arrival at a location named Spirit Point on the crater’s rim. Opportunity drove approximately 13 miles (21 kilometers) since climbing out of the Victoria Crater.

“NASA is continuing to write remarkable chapters in our nation’s story of exploration with discoveries on Mars and trips to an array of challenging new destinations,” NASA Administrator Charles Bolden said. “Opportunity’s findings and data from the upcoming Mars Science Laboratory will play a key role in making possible future human missions to Mars and other places where humans have not yet been.”

Endeavour Crater, which is more than 25 times wider than Victoria Crater, is 14 miles (22 kilometers) in diameter. At Endeavour, scientists expect to see much older rocks and terrains than those examined by Opportunity during its first seven years on Mars. Endeavour became a tantalizing destination after NASA’s Mars Reconnaissance Orbiter detected clay minerals that may have formed in an early warmer and wetter period.

“We’re soon going to get the opportunity to sample a rock type the rovers haven’t seen yet,” said Matthew Golombek, Mars Exploration Rover science team member, at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, Calif. “Clay minerals form in wet conditions so we may learn about a potentially habitable environment that appears to have been very different from those responsible for the rocks comprising the plains.”

The name Spirit Point informally commemorates Opportunity’s twin rover, which stopped communicating in March 2010. Spirit’s mission officially concluded in May.

Geauga’s Observatory Park grand opening August 20

Photo: Oberle Observatory in Geauga Park District's Observatory Park. Photo by James Guilford.
Oberle Observatory in Geauga Park District's Observatory Park. Photo by James Guilford.

A special evening of activities is planned marking the 50th anniversary of the Geauga Park District. The event also serves as the public’s first viewing of its newest park, Observatory Park. Plans call for everything to get underway at 4:00 PM with a park dedication and ribbon-cutting ceremony. Tours, entertainment, a hot dog dinner, and evening concert are planned. The evening culminates in a first-light ceremony at the new Oberle Observatory itself. Click here for the full schedule of events.

9:15 PM: “First Light Ceremony” Dedication and Ribbon-Cutting of the Oberle Observatory and Telescope. The Newtonian reflector boasts a universe-grabbing 25.5-inch mirror created by legendary local astronomer Norman Oberle. Sandy Oberle donated her late husband’s telescope to the Geauga Park District to continue his legacy by opening the heavens to the public. The ceremony will feature the Chagrin Valley Astronomical Society’s Ian Cooper and Sandy Oberle.

9:15 PM – Midnight: Stargazing hosted by the Chagrin Valley Astronomical Society.

Observatory Park, 10610 Clay Street, Montville Township
Event Open to the Public • Free Entertainment and Education for All Ages • Registration is not required. Call: (440) 286-9516 with questions.