NASA Spaceplace Newsletter, September 2016

One Incredible Galaxy Cluster Yields Two Types of Gravitational Lenses

By Ethan Siegel

There is this great idea that if you look hard enough and long enough at any region of space, your line of sight will eventually run into a luminous object: a star, a galaxy or a cluster of galaxies. In reality, the universe is finite in age, so this isn't quite the case. There are objects that emit light from the past 13.7 billion years—99 percent of the age of the universe—but none before that. Even in theory, there are no stars or galaxies to see beyond that time, as light is limited by the amount of time it has to travel.

But with the advent of large, powerful space telescopes that can collect data for the equivalent of millions of seconds of observing time, in both visible light and infrared wavelengths, we can see nearly to the edge of all that's accessible to us.

The most massive compact, bound structures in the universe are galaxy clusters that are hundreds or even thousands of times the mass of the Milky Way. One of them, Abell S1063, was the target of a recent set of Hubble Space Telescope observations as part of the Frontier Fields program. While the Advanced Camera for Surveys instrument imaged the cluster, another instrument, the Wide Field Camera 3, used an optical trick to image a parallel field, offset by just a few arc minutes. Then the technique was reversed, giving us an unprecedentedly deep view of two closely aligned fields simultaneously, with wavelengths ranging from 435 to 1600 nanometers.

With a huge, towering galaxy cluster in one field and no comparably massive objects in the other, the effects of both weak and strong gravitational lensing are readily apparent. The galaxy cluster—over 100 trillion times the mass of our sun—warps the fabric of space. This causes background light to bend around it, converging on our eyes another four billion light years away. From behind the cluster, the light from distant galaxies is stretched, magnified, distorted, and bent into arcs and multiple images: a classic example of strong gravitational lensing. But in a subtler fashion, the less optimally aligned galaxies are distorted as well; they are stretched into elliptical shapes along concentric circles surrounding the cluster.

A visual inspection yields more of these tangential alignments than radial ones in the cluster field, while the parallel field exhibits no such shape distortion. This effect, known as weak gravitational lensing, is a very powerful technique for obtaining galaxy cluster masses independent of any other conditions. In this serendipitous image, both types of lensing can be discerned by the naked eye. When the James Webb Space Telescope launches in 2018, gravitational lensing may well empower us to see all the way back to the very first stars and galaxies.

If you’re interested in teaching kids about how these large telescopes “see,” be sure to see our article on this topic at the NASA Space Place:

Image credit: NASA, ESA and Jennifer Lotz (STScI) Galaxy cluster Abell S1063 (left) as imaged with the Hubble Space Telescope as part of the Frontier Fields program. The distorted images of the background galaxies are a consequence of the warped space dues to Einstein's general relativity; the parallel field (right) shows no such effects.

NASA Spaceplace Newsletter, August 2016

Is there a super-Earth in the Solar System out beyond Neptune?

By Ethan Siegel

When the advent of large telescopes brought us the discoveries of Uranus and then Neptune, they also brought the great hope of a Solar System even richer in terms of large, massive worlds. While the asteroid belt and the Kuiper belt were each found to possess a large number of substantial icy-and-rocky worlds, none of them approached even Earth in size or mass, much less the true giant worlds. Meanwhile, all-sky infrared surveys, sensitive to red dwarfs, brown dwarfs and Jupiter-mass gas giants, were unable to detect anything new that was closer than Proxima Centauri. At the same time, Kepler taught us that super-Earths, planets between Earth and Neptune in size, were the galaxy's most common, despite our Solar System having none.

The discovery of Sedna in 2003 turned out to be even more groundbreaking than astronomers realized. Although many Trans-Neptunian Objects (TNOs) were discovered beginning in the 1990s, Sedna had properties all the others didn't. With an extremely eccentric orbit and an aphelion taking it farther from the Sun than any other world known at the time, it represented our first glimpse of the hypothetical Oort cloud: a spherical distribution of bodies ranging from hundreds to tens of thousands of A.U. from the Sun. Since the discovery of Sedna, five other long-period, very eccentric TNOs were found prior to 2016 as well. While you'd expect their orbital parameters to be randomly distributed if they occurred by chance, their orbital orientations with respect to the Sun are clustered extremely narrowly: with less than a 1-in-10,000 chance of such an effect appearing randomly.

Whenever we see a new phenomenon with a surprisingly non-random appearance, our scientific intuition calls out for a physical explanation. Astronomers Konstantin Batygin and Mike Brown provided a compelling possibility earlier this year: perhaps a massive perturbing body very distant from the Sun provided the gravitational "kick" to hurl these objects towards the Sun. A single addition to the Solar System would explain the orbits of all of these long-period TNOs, a planet about 10 times the mass of Earth approximately 200 A.U. from the Sun, referred to as Planet Nine. More Sedna-like TNOs with similarly aligned orbits are predicted, and since January of 2016, another was found, with its orbit aligning perfectly with these predictions.

Ten meter class telescopes like Keck and Subaru, plus NASA's NEOWISE mission, are currently searching for this hypothetical, massive world. If it exists, it invites the question of its origin: did it form along with our Solar System, or was it captured from another star's vicinity much more recently? Regardless, if Batygin and Brown are right and this object is real, our Solar System may contain a super-Earth after all.

Image: A possible super-Earth/mini-Neptune world hundreds of times more distant than Earth is from the Sun. Image credit: R. Hurt / Caltech (IPAC)

HPSP Star Party Saturday Night June 4

Weather permitting, the first GAAC star party of the year is set for Saturday night, June 4, from sunset to 10 pm. All are invited, and of course there is no cost. We'll have telescopes set up next to the Vistor Center to view Mars, Jupiter, galaxies, nebulae, colorful double stars, and more! 

Please park in the paved lot off of Gott Ave and walk up the hill to the Visitor Center. We'll see you there!

NASA Spaceplace Newsletter, March 2016

Gravitational Wave Astronomy Will Be The Next Great Scientific Frontier

By Ethan Siegel

Imagine a world very different from our own: permanently shrouded in clouds, where the sky was never seen. Never had anyone see the Sun, the Moon, the stars or planets, until one night, a single bright object shone through. Imagine that you saw not only a bright point of light against a dark backdrop of sky, but that you could see a banded structure, a ringed system around it and perhaps even a bright satellite: a moon. That's the magnitude of what LIGO (the Laser Interferometer Gravitational-wave Observatory) saw, when it directly detected gravitational waves for the first time.

An unavoidable prediction of Einstein's General Relativity, gravitational waves emerge whenever a mass gets accelerated. For most systems -- like Earth orbiting the Sun -- the waves are so weak that it would take many times the age of the Universe to notice. But when very massive objects orbit at very short distances, the orbits decay noticeably and rapidly, producing potentially observable gravitational waves. Systems such as the binary pulsar PSR B1913+16 [the subtlety here is that binary pulsars may contain a single neutron star, so it’s best to be specific], where two neutron stars orbit one another at very short distances, had previously shown this phenomenon of orbital decay, but gravitational waves had never been directly detected until now.

When a gravitational wave passes through an objects, it simultaneously stretches and compresses space along mutually perpendicular directions: first horizontally, then vertically, in an oscillating fashion. The LIGO detectors work by splitting a laser beam into perpendicular “arms,” letting the beams reflect back and forth in each arm hundreds of times (for an effective path lengths of hundreds of km), and then recombining them at a photodetector. The interference pattern seen there will shift, predictably, if gravitational waves pass through and change the effective path lengths of the arms. Over a span of 20 milliseconds on September 14, 2015, both LIGO detectors (in Louisiana and Washington) saw identical stretching-and-compressing patterns. From that tiny amount of data, scientists were able to conclude that two black holes, of 36 and 29 solar masses apiece, merged together, emitting 5% of their total mass into gravitational wave energy, via Einstein's E = mc2.

During that event, more energy was emitted in gravitational waves than by all the stars in the observable Universe combined. The entire Earth was compressed by less than the width of a proton during this event, yet thanks to LIGO's incredible precision, we were able to detect it. At least a handful of these events are expected every year. In the future, different observatories, such as NANOGrav (which uses radiotelescopes to the delay caused by gravitational waves on pulsar radiation) and the space mission LISA will detect gravitational waves from supermassive black holes and many other sources. We've just seen our first event using a new type of astronomy, and can now test black holes and gravity like never before.

Image credit: Observation of Gravitational Waves from a Binary Black Hole Merger B. P. Abbott et al., (LIGO Scientific Collaboration and Virgo Collaboration), Physical Review Letters 116, 061102 (2016). This figure shows the data (top panels) at the Washington and Louisiana LIGO stations, the predicted signal from Einstein's theory (middle panels), and the inferred signals (bottom panels). The signals matched perfectly in both detectors.

GAAC Holiday Party Program Note

Wow, do we ever have an amazing treat for you at our December 11 GAAC holiday party.

We'll have all kinds of goodies to eat and drink, of course, and lots of good company and conversation, of course, but the big news is all about who we've got speaking: Babak Tafreshi, the creator of "The World At Night," will discuss his work and present a stunning program of his unique astrophotographs. Babak is an internationally known photographer and a tireless advocate for astronomy and the preservation of dark skies.

Here is just a small section of his official Bio from

"TWAN founder and leader, Babak Tafreshi is an award winning photographer working with the National Geographic, Sky&Telescope magazine, and the European Southern Observatory (ESO). Babak is also a freelance science journalist and astronomy communicator using all media. Born in 1978 in Tehran he is based in Boston, United States, but could be anywhere on the planet, from the Sahara to the Himalayas or Antarctica. He is a board member of Astronomers Without Borders organization, an international organization to bridge between cultures and connect people around the world through their common interest to astronomy. He received the 2009 Lennart Nilsson Award, the world’s most recognized award for scientific photography, for his global contribution to night sky photography."

Holy cow, you'll want to come early for this one. The joint will be packed. This will be a GAAC party to remember. See our Contact page for directions; see our home page for other club details.

GAAC November 13 Program Note

Our November meeting will be held on Friday November 13, at 8:00 pm, at the Lanesville Community Center. Old friend Jim Koerth will host a profound, colorful exposition on the human investigation into the origin of all things. When and how did the universe begin?  As we peer farther and farther back in time with our giant telescopes, a global group of astronomers wants to answer that question by looking as far back as a large telescope will let us see.

Jim will introduce us all, via DVD, to a prime mover in the creation of the Giant Magellan Telescope, now under construction in South America.  Share in the bold vision about the discoveries the GMT could possibly make about our universe.  A Q&A and discussion session will follow the brief video.

Come in and enjoy the fall musings of GAACsters from far and wide, and become part of the conversation. There will be pie.

The club meets at 8:00 pm on the second Friday of every month at the Lanesville Community Center.  See our Contact page for a map and driving directions. Parking is free, there are no dues or fees, and everyone is welcome. Come on in -- you'll have a great time!

Come to the October 9 GAAC Meeting -- Our 12th Anniversary!

The Gloucester Area Astronomy Club registered the domain name on October 13 2003, which makes the Friday October 9 meeting our twelfth anniversary! Come on in and help us celebrate, along with some of our accomplished stable of astrophotographers as they each show off examples of their most recent work, including some shots they've been saving for just this occasion.

We'll see a bunch of terrific pictures, and hear the how's and why's as well, as each photographer explains each image, its significance, and some details of the hunt that produced it.

This will be a colorful, entertaining and elucidating night of astrophotography, science, friends, coffee and cake, and of course lots of great conversation to boot. Don't miss it!

GAAC meets at 8:00 on the second Friday of every month at the Lanesville Community Center, 8 Vulcan Street Gloucester. See our Contact page for directions. There is no cost, and parking is free. For more info on the club, see our Facebook page,, or follow us on Twitter @gaacster. All are welcome, and no prior knowledge of astronomy is needed to have a great time!

Sky Object of the Month – September 2015

S Cepheii – Carbon Star in Cepheus
by Glenn Chaple

This past August 15th, I presented a talk on carbon stars at the Stellafane Convention. The library at the McGregor Observatory, which served as the setting, hosts a typical audience of 12 to 20. This time, more than 30 Stellafaners showed up. The topic was obviously one of intense interest!

The reason is obvious to anyone who has ever looked at a carbon star like R Leporis (“Hind’s Crimson Star”), T Lyrae, or V Aquilae. At certain times, they can appear red – drop-of- blood red!

Popular fare for backyard astronomers over a century ago, carbon stars have enjoyed a resurgence in popularity, particularly with individuals seeking a change from the usual deep-sky fare of nebulae. clusters, and galaxies. They have become so popular that the Astronomical League recently initiated a carbon star observing program that lists 100 of these cosmic rubies.

Like its kindred carbon stars, of which nearly 7000 have been catalogued, S Cephei is a red supergiant with a ‘sooty” carbon-laced outer atmosphere that enhances its ruddy appearance. Typical of its stellar class, it varies in brightness, ranging from 7th to 11th magnitude in a period averaging 485 days.

Lest I be accused of false advertisement, I should point out that not all carbon stars are ruby red. The color you see will depend on your vision, the nature of binocular or telescope used, sky conditions, and the star’s magnitude (carbon stars tend to be reddest when near minimum brightness). At the very least, a carbon star will shine with a rich golden yellow hue.

The accompanying finder charts point the way to S Cephei. A line from gamma (γ) to the wide pair rho (ρ) and 28 Cephei and extended an equal distance beyond brings you to a triangle of 7th magnitude stars perched atop a 6th magnitude star labeled 59 (its magnitude without decimals) on Chart B. Chart C will help you star-hop from the triangle to S Cephei. Magnitudes of surrounding stars are added (decimals omitted).

You’ll find more information on S Cephei at The Astronomical League’s Carbon Star Program is described at

Finder Charts A (; Finder Chart B.  (AAVSO); Finder Chart C. (AAVSO)