The Invisible Galaxy

A new form of diffuse galaxy has been discovered inside the Coma Cluster. This place is made 99.99% of dark matter, totally invisible as it doesn’t interact with light.

The galaxy is known as Dragonfly 44 and was discovered by astronomers Pieter van Dokkum and his colleagues.

The way star systems orbit around the center of a galaxy is inexplicable with “normal” physics. To account for the velocity variations and patterns we need to add a new ingredient to the gravitational pot: dark matter.

Dragonfly 44 in particular has so few stars that were the dark matter to be taken away, the galaxy would fly apart the same way you’d go flying if the cord holding the swing to a swing set were severed.

(Image credit: NASA, JPL-CalTech and L. Jenkins

A long-dead star

This Hubble Space Telescope image captures the remnants of a long-dead star. These rippling wisps of ionised gas, named DEM L316A, are located some 160 000 light-years away within one of the Milky Way’s closest galactic neighbours — the Large Magellanic Cloud (LMC).

The explosion that formed DEM L316A was an example of an especially energetic and bright variety of supernova, known as a Type Ia. Such supernova events are thought to occur when a white dwarf star steals more material than it can handle from a nearby companion, and becomes unbalanced. The result is a spectacular release of energy in the form of a bright, violent explosion, which ejects the star’s outer layers into the surrounding space at immense speeds. As this expelled gas travels through the interstellar material, it heats it up and ionise it, producing the faint glow that Hubble’s Wide Field Camera 3 has captured here.

Credit: ESA/Hubble & NASA, Y. Chu
The Observable Universe Is Actually Millions of Light-Years Smaller Than We Thought

One thing we’re always doing as a species is expanding our knowledge of the heavens. We send out probes, robots, satellites, spacecraft, all to map out and add to our ever-expanding picture of what the Universe looks like.

But what if that picture suddenly became smaller? That is exactly what happened when new data from the Planck satellite tightened our previous notions of the observable universe, shrinking its area by 0.7%.

If you’ve never realized, we don’t actually see all of the stars in the Universe. If we did, night time sky would be a whole lot brighter. Instead, we see everything within a particular radius, the particle horizon. Any particle of light emitted outside that particle horizon is too far to have reached us.

So if we want to know just how large the observable universe is, we just have to figure out the distance between us and that particle horizon, right?

As it turns out, not quite.

The universe, specifically spacetime, is continuously expanding, with points in the universe moving further apart. This not only changes the distance between objects but also how fast light is moving in the universe. 

The movement of spacetime has an effect on which photons reach us and can be observed.

So how do you calculate the radius? Back in 2003, scientists came up with an equation that took an event called “the recombination” as a reference point in the universe’s history. They combined that with the rate of the expansion of the universe and several other factors, in the end coming up with a number.

Back in 2003, that number was a radius of 45.66 billion light-years. Now, new data revealed a far more accurate number: 45.34 billion light-years.

“A difference of 320 million light-years might be peanuts on the cosmic scale, but it does make our knowable universe a little bit cozier,” Nick Tomasello from the University of the Sciences in Philadelphia writes over at Medium.

The study has been accepted for publication in an upcoming edition of Advances in Astrophysics.

Not Really Starless at Saturn

Saturn’s main rings, along with its moons, are much brighter than most stars. As a result, much shorter exposure times (10 milliseconds, in this case) are required to produce an image and not saturate the detectors of the imaging cameras on NASA’s Cassini spacecraft. A longer exposure would be required to capture the stars as well. Cassini has captured stars on many occasions, especially when a target moon is in eclipse, and thus darker than normal.

Dione (698 miles, 1123 kilometers across) and Epimetheus (70 miles, 113 kilometers across) are seen in this view, above the rings at left and right respectively.

Credit: NASA

What dark structures arise from the Pelican Nebula? Visible as a bird-shaped nebula toward the constellation of a bird (Cygnus, the Swan), the Pelican Nebula is a place dotted with newly formed stars but fouled with dark dust. These smoke-sized dust grains formed in the cool atmospheres of young stars and were dispersed by stellar winds and explosions. Impressive Herbig-Haro jets are seen emitted by a star on the right that is helping to destroy the light year-long dust pillar that contains it. The featured image was scientifically-colored to emphasize light emitted by small amounts of ionized nitrogen, oxygen, and sulfur in the nebula made predominantly of hydrogen and helium. The Pelican Nebula (IC 5067 and IC 5070) is about 2,000 light-years away and can be found with a small telescope to the northeast of the bright star Deneb.

Object Names: Pelican Nebula, IC 5067, IC 5070

Imagte Type: Astronomical

Credit: Larry Van Vleet (LVVASTRO)

Time And Space


Ask Ethan: How Do We Know The Universe Is 13.8 Billion Years Old?

“You’ve heard the story before: the Universe began with the Big Bang 13.8 billion years ago, and formed atoms, stars, galaxies, and eventually planets with the right ingredients for life. Looking at distant locations in the Universe is also looking back in time, and somehow, through the power of physics and astronomy, we’ve figured out not only how the Universe began, but its age. But how do we know how old the Universe is? That what Thys Hauptfleisch wants to know for this week’s Ask Ethan:

Ethan, how was the 13.8 billion years calculated? (In English please!)”

There’s a unique relationship between everything that exists in the Universe today – the stars and galaxies, the large-scale structure, the leftover glow from the Big Bang, the expansion rate, etc. – and the amount of time that’s passed since it all began. When it comes to our Universe, there really was a day without a yesterday, but how do we know exactly how much time has passed between then and now? There are two ways: one complex and one simple. The complex way is to determine all the matter and energy components making up the Universe, to measure how the Universe has expanded over the entirety of its cosmic history, and then, in the context of the Big Bang, to deduce how old the Universe must be. The other is to understand stars, measure them, and determine how old the oldest ones are.

The complex answer is more accurate, but more importantly, they both agree with each other. Get the details on this week’s Ask Ethan!

NASA Astronomy Picture of the Day 2016 August 27 

Lunar Orbiter Earthset 

August 10th was the 50th anniversary of the launch of Lunar Orbiter 1. It was the first of five Lunar Orbiters intended to photograph the Moon’s surface to aid in the selection of future landing sites. That spacecraft’s camera captured the data used in this restored, high-resolution version of its historic first image of Earth from the Moon on August 23, 1966 while on its 16th lunar orbit. Hanging almost stationary in the sky when viewed from the lunar surface, Earth appears to be setting beyond the rugged lunar horizon from the perspective of the orbiting spacecraft. Two years later, the Apollo 8 crew would record a more famous scene in color: Earthrise from lunar orbit.

Thomas Wright - A Central Section of Creation with the All-Seeing Eye, “An Original Theory or New Hypothesis of the Universe”, 1750.

Combining astronomical and theological concepts, Thomas Wright proposed a version of the universe where the stars are arranged in a spherical shell separated from a supernatural center by a huge gap. The stars are in motion about the center, like planets. And the stars form individual solar systems that make up the Milky Way galaxy. The center of Wright’s universe is the domain of a divine Presence, who is responsible for all the motion of the stars. Wright’s universe is modified by Immanuel Kant, who saw the stars not as an unordered crowd, but an ordered system lying in a plan moving by motions guided by Newton’s laws of motion.


The Orbit Pavilion is a joint project between The Studio at JPLSTUDIOKCA and Shane Myrbeck.

About the project:

In this installation, we’ve created a shell that allows you to listen to the movement of spacecraft passing overhead hundreds of miles above you as they monitor our planet’s ever-changing land, sky and sea. By pairing the trajectory data of each spacecraft to artistically created sounds, you can listen to the moving spacecraft much like you hear a plane passing over your head.

(NASA)  In In the Center of the Lagoon Nebula
Image Credit: Hubble Legacy Archive, NASA, ESA - Processing & Licence: Judy Schmidt

The center of the Lagoon Nebula is a whirlwind of spectacular star formation. Visible near the image center, at least two long funnel-shaped clouds, each roughly half a light-year long, have been formed by extreme stellar winds and intense energetic starlight. The tremendously bright nearby star, Herschel 36, lights the area. Walls of dust hide and redden other hot young stars. As energy from these stars pours into the cool dust and gas, large temperature differences in adjoining regions can be created generating shearing winds which may cause the funnels. This picture, spanning about 5 light years, combines images taken by the orbiting Hubble Space Telescope. The Lagoon Nebula, also known as M8, lies about 5,000 light years distant toward the constellation of Sagittarius.