Sep 13

One Incredible Galaxy Cluster Yields Two Types of Gravitational Lenses

By Ethan SiegelSP-Logo-300.en

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:


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. Image credit: NASA, ESA and Jennifer Lotz (STScI)

This article is provided by NASA Space Place. With articles, activities, crafts, games, and lesson plans, NASA Space Place encourages everyone to get excited about science and technology. Visit to explore space and Earth science!

Sep 01

What’s Up in the Sky

What’s Up in the Sky – September, 2016

Earth’s Cousin May Be Very Close By

Algebra doesn’t change much. The Algebra I taught at St. Augustine Seminary HS in 1970 was pretty much the same as the Algebra I taught at Fennville HS in 2002. Astronomy, on the other hand, does change . . . drastically and profoundly. Sure, solving the Four Color Theorem (a famous problem in mathematics that was proved in 1976) was an example of change, but it didn’t alter the basic framework of mathematics. On the other hand, recently astronomers have made discoveries that drastically changed how we view the universe.

For example, we have known that the universe is expanding since Edwin Hubble’s observations in the 1920’s. This immediately brought up the fate of the universe – would it keep expanding forever, reach equilibrium, or collapse back on itself? Then in 1998 we discovered that the expansion was actually accelerating and, in an attempt to explain the observations, astronomers have been searching for dark matter and dark energy ever since. Now, that’s a BIG change.

Then there are exoplanets, planets that orbit stars other than the Sun. In 1984 a disc of material was shown to exist around the star Beta Pictoris, confirming current theories of planetary formation. Then, in October of 1995, the discovery was made of the first planet (a Jupiter – sized object with a very short “year”) in orbit around another star.

We now know of 3,374 exoplanets and estimate there to be on average two for every star in the Milky Way. That doesn’t mean all stars have planets, some may have eight or ten and many may have zero. But the latest discovery sheds some light on the question: how common are planets?

Last Wednesday, a group of thirty-one astronomers in the UK announced the discovery of a planet orbiting the star Proxima Centauri, which my former Astronomy students will tell you is the star closest to us in the galaxy. In addition to its close proximity to us (which explains the name of the parent star), what is even more astonishing is that this planet might be quite similar to our own planet, Earth.

The Keppler Space Telescope has shown that most of our galaxy’s planets are terrestrial, that is, Earth-like, small and rocky rather than gas giants like Jupiter. The newly detected planet is at least 1.3 times the mass of Earth and lies in the “goldilocks zone”, where its temperature allows the presence of liquid water on its surface.

However, we don’t know the composition of the planet nor its habitability. New instruments under construction should be able to image the object directly, giving us insights into these questions.

No matter the final analysis, it is a very exciting discovery, one that should allow us an even better understanding of what’s up in the sky.

This month in history:
∙ Sept. 3: Last two Apollo Moon landings canceled by NASA – 1970
∙ Sept. 8: Voyager 1 launched – 1977
∙ Sept. 18: Photo of Earth and Moon together in space taken by Voyager 1 – 1977
∙ Sept. 20: Wernher von Braun arrives in US – 1945
∙ Sept. 23: Premier of “The Jetsons” – 1962
∙ Sept. 30: End of daily communication with Pioneer 11 – 1995

Aug 21

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

By Ethan Siegel

When the aSP-Logo-300.endvent 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.


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

This article is provided by NASA Space Place. With articles, activities, crafts, games, and lesson plans, NASA Space Place encourages everyone to get excited about science and technology. Visit to explore space and Earth science!

May 15

NOAA’s Joint Polar Satellite System (JPSS) to revolutionize Earth-watching

By Ethan Siegel

If you wSP-Logo-300.enant to collect data with a variety of instruments over an entire planet as quickly as possible, there are two trade-offs you have to consider: how far away you are from the world in question, and what orientation and direction you choose to orbit it. For a single satellite, the best of all worlds comes from a low-Earth polar orbit, which does all of the following:

• orbits the Earth very quickly: once every 101 minutes,
• is close enough at 824 km high to take incredibly high-resolution imagery,
• has five separate instruments each probing various weather and climate phenomena,
• and is capable of obtaining full-planet coverage every 12 hours.

The type of data this new satellite – the Joint Polar Satellite System-1 (JPSS-1) — will take will be essential to extreme weather prediction and in early warning systems, which could have severely mitigated the impact of natural disasters like Hurricane Katrina. Each of the five instruments on board are fundamentally different and complementary to one another. They are:

1. The Cross-track Infrared Sounder (CrIS), which will measure the 3D structure of the atmosphere, water vapor and temperature in over 1,000 infrared spectral channels. This instrument is vital for weather forecasting up to seven days in advance of major weather events.

2. The Advanced Technology Microwave Sounder (ATMS), which assists CrIS by adding 22 microwave channels to improve temperature and moisture readings down to 1 Kelvin accuracy for tropospheric layers.

3. The Visible Infrared Imaging Radiometer Suite (VIIRS) instrument, which takes visible and infrared pictures at a resolution of just 400 meters (1312 feet), enables us to track not just weather patterns but fires, sea temperatures, nighttime light pollution as well as ocean-color observations.

4. The Ozone Mapping and Profiler Suite (OMPS), which measures how the ozone concentration varies with altitude and in time over every location on Earth’s surface. This instrument is a vital tool for understanding how effectively ultraviolet light penetrates the atmosphere.

5. Finally, the Clouds and the Earth’s Radiant System (CERES) will help understand the effect of clouds on Earth’s energy balance, presently one of the largest sources of uncertainty in climate modeling.

The JPSS-1 satellite is a sophisticated weather monitoring tool, and paves the way for its’ sister satellites JPSS-2, 3 and 4. It promises to not only provide early and detailed warnings for disasters like hurricanes, volcanoes and storms, but for longer-term effects like droughts and climate changes. Emergency responders, airline pilots, cargo ships, farmers and coastal residents all rely on NOAA and the National Weather Service for informative short-and-long-term data. The JPSS constellation of satellites will extend and enhance our monitoring capabilities far into the future.


Images credit: an artist’s concept of the JPSS-2 Satellite for NOAA and NASA by Orbital ATK (top); complete temperature map of the world from NOAA’s National Weather Service (bottom).

This article is provided by NASA Space Place. With articles, activities, crafts, games, and lesson plans, NASA Space Place encourages everyone to get excited about science and technology. Visit to explore space and Earth science!

Apr 15

Hubble Shatters The Cosmic Record For Most Distant Galaxy

By ESP-Logo-300.enthan Siegel
The farther away you look in the distant universe, the harder it is to see what’s out there. This isn’t simply because more distant objects appear fainter, although that’s true. It isn’t because the universe is expanding, and so the light has farther to go before it reaches you, although that’s true, too. The reality is that if you built the largest optical telescope you could imagine — even one that was the size of an entire planet — you still wouldn’t see the new cosmic record-holder that Hubble just discovered: galaxy GN-z11, whose light traveled for 13.4 billion years, or 97% the age of the universe, before finally reaching our eyes.

There were two special coincidences that had to line up for Hubble to find this: one was a remarkable technical achievement, while the other was pure luck. By extending Hubble’s vision away from the ultraviolet and optical and into the infrared, past 800 nanometers all the way out to 1.6 microns, Hubble became sensitive to light that was severely stretched and redshifted by the expansion of the universe. The most energetic light that hot, young, newly forming stars produce is the Lyman-α line, which is produced at an ultraviolet wavelength of just 121.567 nanometers. But at high redshifts, that line passed not just into the visible but all the way through to the infrared, and for the newly discovered galaxy, GN-z11, its whopping redshift of 11.1 pushed that line all the way out to 1471 nanometers, more than double the limit of visible light!

Hubble itself did the follow-up spectroscopic observations to confirm the existence of this galaxy, but it also got lucky: the only reason this light was visible is because the region of space between this galaxy and our eyes is mostly ionized, which isn’t true of most locations in the universe at this early time! A redshift of 11.1 corresponds to just 400 million years after the Big Bang, and the hot radiation from young stars doesn’t ionize the majority of the universe until 550 million years have passed. In most directions, this galaxy would be invisible, as the neutral gas would block this light, the same way the light from the center of our galaxy is blocked by the dust lanes in the galactic plane. To see farther back, to the universe’s first true galaxies, it will take the James Webb Space Telescope. Webb’s infrared eyes are much less sensitive to the light-extinction caused by neutral gas than instruments like Hubble. Webb may reach back to a redshift of 15 or even 20 or more, and discover the true answer to one of the universe’s greatest mysteries: when the first galaxies came into existence!


Images credit:  (top); NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz) (bottom), of the galaxy GN-z11, the most distant and highest-redshifted galaxy ever discovered and spectroscopically confirmed thus far.

This article is provided by NASA Space Place. With articles, activities, crafts, games, and lesson plans, NASA Space Place encourages everyone to get excited about science and technology. Visit to explore space and Earth science!

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