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Why scientists want to find a pulsar orbiting a black hole

View larger. | Via Skascience

Artist’s concept of black hole via SKA Organization/Swinburne Astronomy Productions

Pulsars are the most precise “clocks” in the known universe. They emit signals with such clocklike regularity that scientists use them in tests of Einstein’s general theory of relativity, which explains how gravity works. These tests of relativity work best in star systems where pulsars orbit with other pulsars or with white dwarfs. But what scientists really wish to find – in order to carry their tests of Einstein’s theory of gravity to the highest possible level of precision – is a pulsar orbiting a black hole. And that, my friends, is very, very rare.

How galaxies evolve in the cosmic web

Galaxies are distributed along a cosmic web in the universe. “Mpc/h” is a unit of galactic distance (1 Mpc/h is more than 3.2 million light-years). Image credit: Volker Springel, Virgo Consortium.

Artist’s illustration of the “cosmic web.” The web walls are galaxies in clusters. Filaments are woven throughout, like threads. Mpc/h is a unit of distance, with 1 Mpc/h more than 3.2 million light-years. Image via Volker Springel, Virgo Consortium.

An international team of researchers applied a new computational method to existing data on the large-scale structure of the universe, or “cosmic web.” Their work indicates that the filaments that bridge the denser regions of the web have a much higher chance of actively forming stars. In other words, in the distant universe, galaxy evolution seems to have been accelerated in the filaments.

Glacier melt rate in West Antarctica tripled in last decade

View larger. | Antarctic glaciers, via the American Geophysical Union.

View larger. | Glaciers in West Antarctica as seen during a NASA Operation IceBridge campaign on October 29, 2014. Photo via NASA/Michael Studinger and via AGU.

The melt rate of glaciers in the fastest-melting region of Antarctica has tripled during the last decade, according to a comprehensive, 21-year analysis that reconciles four different techniques previously used to measure Antarctic ice melting.

Lifeform of the week: Horseshoe crab

Image Credit: H Dragon

Image Credit: H Dragon

Walking along the beach, I saw the discarded shell of a most unfamiliar creature. It was as big as a salad serving bowl and looked like it fallen through a wormhole from a prehistoric time when animals were bigger and weirder. After some minimal description and “this big” gesturing, the locals enlightened me. These were shells of the Atlantic horseshoe crab, and if the animal looks like it comes from another era, that’s because it does.

Scientists identify mysterious killer of millions of sea stars

A sunflower sea star (Pycnopodium helianthoides). Image Credit: Kevin Lafferty, U.S. Geological Survey.

A healthy sunflower sea star (Pycnopodium helianthoides). Image Credit: Kevin Lafferty, U.S. Geological Survey.

Scientists say that a densovirus is the likely culprit behind sea-star wasting disease. The disease has killed millions of sea stars along the west coast of North America since 2013.

Everything you need to know: December solstice 2014

Around the time of the winter solstice, watch for late dawns, early sunsets, and the low arc of the sun across the sky each day. Notice your noontime shadow, the longest of the year. Photo via Serge Arsenie on Flickr.

The solstice happens at the same instant for all of us, everywhere on Earth. In 2014, the December solstice comes on December 21 at 5:03 p.m. CST. That’s December 21 at 23:03 UTC. It’s when the sun on our sky’s dome reaches its farthest southward point for the year.

Days of darkness this December? Of course not.

This incredible image of the night side of Earth is a composite of data gathered by the Suomi NPP satellite in April and October 2012 and mapped over previous imagery of the whole Earth.  Image via NASA/NOAA.

Night side of Earth. Is Earth totally dark when it’s night for you? No. Earth is always half illuminated by sunlight. Notice the crescent of illumination on one edge in this photo. If you were on the other side of Earth when the images used in this composite were acquired, you’d see Earth shining brightly in reflected sunlight, aka daylight. Image via NASA/NOAA.

Question: Will Earth experience six (or three) days of darkness this December?

Answer: No.

We at EarthSky have received many questions already about the so-called days of darkness supposedly announced by NASA and supposedly coming up this month. This rumor has spread like wildfire, as did the same rumor in 2011, which called for days of darkness caused by the erstwhile Comet Elenin. Is it true? Of course not.

What happened when the comet swept past Mars

Ultraviolet image of Comet Siding Spring via MAVEN

Ultraviolet image of Comet Siding Spring via MAVEN

On October 19, 2014, Comet C/2013A1 Siding Spring passed only 140,000 kilometers / 87,000 miles of Mars, closer than any known comet in recorded history, making its first foray into the inner solar system after a seven-million-year journey from the postulated Oort Cloud, some one-light year from the sun. There were observations from the surface of Mars, and from orbit. There is a potential twist to the comet’s story, with this comet potentially even more remarkable than first suspected. Plus there was a meteor shower as seen from Mars’ surface. All of this is described inside.

Dolphins use specific whistles as names

Image credit: Shutterstock / Willyam Bradberry

Image credit: Shutterstock / Willyam Bradberry

Bottlenose dolphins in Africa use signature whistles to identify each other, similar to the way humans use names, say scientists.

Lifeform of the week: Cranberries

My first encounters with cranberries were in the form of cranberry sauce, specifically the canned variety. But cranberries are more than just a holiday condiment.