Evidence for supernovas near Earth

Aug 27, 2014 by Dr. Tony Phillips
Evidence for Supernovas Near Earth
The Local Bubble and the Galactic Neighborhood. Credit: Illustration Credit & Copyright: Linda Huff (American Scientist), Priscilla Frisch (U. Chicago)

Once every 50 years, more or less, a massive star explodes somewhere in the Milky Way. The resulting blast is terrifyingly powerful, pumping out more energy in a split second than the sun emits in a million years. At its peak, a supernova can outshine the entire Milky Way.

It seems obvious that you wouldn't want a exploding near Earth. Yet there is growing evidence that one did—actually, more than one. About 10 million years ago, a nearby cluster of supernovas went off like popcorn. We know because the explosions blew an enormous bubble in the interstellar medium, and we're inside it.

Astronomers call it "the Local Bubble." It is peanut-shaped, about 300 light years long, and filled with almost nothing. Gas inside the bubble is very thin (0.001 atoms per cubic centimeter) and very hot (roughly a million degrees)—a sharp departure from ordinary interstellar material.

The Local Bubble was discovered gradually in the 1970s and 1980s. Optical and radio astronomers looked carefully for interstellar gas in our part of the galaxy, but couldn't find much in Earth's neighborhood. Meanwhile, x-ray astronomers were getting their first look at the sky using sounding rockets and orbiting satellites, which revealed a million-degree x-ray glow coming from all directions. It all added up to Earth being inside a bubble of hot gas blown by exploding stars.

However, not all researchers agreed.

"Within the last decade, some scientists have been challenging the [supernova] interpretation, suggesting that much or all of the soft X-ray diffuse background is instead a result of charge exchange," says F. Scott Porter of the Goddard Space Flight Center.

"Charge exchange": Basically, it happens when the electrically-charged solar wind comes into contact with a neutral gas. The solar wind can steal electrons from the neutral gas, resulting in an X-ray glow that looks a lot like the glow from an old supernova. Charge exchange has been observed many times in comets.

So, is the X-ray glow that fills the sky a sign of peaceful "charge exchange" in the or evidence of terrifying explosions in the distant past?

To find out, an international team researchers including Porter and led by physics professor Massimiliano Galeazzi at the University of Miami in Coral Gables, developed an X-ray detector that could distinguish between the two possibilities. The device was named DXL, for Diffuse X-ray emission from the Local Galaxy.

On Dec. 12, 2012, DXL launched from White Sands Missile Range in New Mexico atop a NASA Black Brant IX sounding rocket, reaching a peak altitude of 160 miles and spending five minutes above Earth's atmosphere. That was all the time they needed to measure the amount of "charge exchange" X-rays inside the solar system.

The results, published online in the journal Nature on July 27, indicate that only about 40 percent of the soft X-ray background originates within the solar system. The rest must come from a Local Bubble of hot gas, the relic of ancient supernovas outside the solar system.

Obviously, those supernovas were not close enough to exterminate life on Earth—but they were close enough to wrap our solar system in a bubble of hot gas that persists millions of years later.

"This is a significant discovery,' said Galeazzi. "[It] affects our understanding of the area of the galaxy close to the sun, and can, therefore, be used as a foundation for future models of the galaxy structure."

Galeazzi and collaborators are already planning the next flight of DXL, which will include additional instruments to better characterize the emission. The launch is currently planned for December 2015.

Explore further: Evidence of a local hot bubble carved by a supernova

add to favorites email to friend print save as pdf

Related Stories

Evidence of a local hot bubble carved by a supernova

Jul 30, 2014

I spent this past weekend backpacking in Rocky Mountain National Park, where although the snow-swept peaks and the dangerously close wildlife were staggering, the night sky stood in triumph. Without a fire, ...

The source of the sky's X-ray glow

Jul 27, 2014

In findings that help astrophysicists understand our corner of the galaxy, an international research team has shown that the soft X-ray glow blanketing the sky comes from both inside and outside the solar system.

DXL: NASA launching X-ray emission mission

Dec 10, 2012

NASA will launch an astrophysics mission to study the Diffuse X-ray emission from the Local galaxy (DXL) December 9 from the White Sands Missile Range in New Mexico. The goal of this flight is to identify ...

Image: Pulsar encased in a supernova bubble

Jun 02, 2014

(Phys.org) —Massive stars end their lives with a bang: exploding as spectacular supernovas, they release huge amounts of mass and energy into space. These explosions sweep up any surrounding material, creating ...

Dwarf galaxy caught ramming into a large spiral

Aug 14, 2013

Observations with NASA's Chandra X-ray Observatory have revealed a massive cloud of multimillion-degree gas in a galaxy about 60 million light years from Earth. The hot gas cloud is likely caused by a collision ...

Recommended for you

Finding hints of gravitational waves in the stars

5 hours ago

Scientists have shown how gravitational waves—invisible ripples in the fabric of space and time that propagate through the universe—might be "seen" by looking at the stars. The new model proposes that ...

How gamma ray telescopes work

6 hours ago

Yesterday I talked about the detection of gamma ray bursts, intense blasts of gamma rays that occasionally appear in distant galaxies. Gamma ray bursts were only detected when gamma ray satellites were put ...

The frequency of high-energy gamma ray bursts

8 hours ago

In the 1960s a series of satellites were built as part of Project Vela.  Project Vela was intended to detect violations of the 1963 ban on above ground testing of nuclear weapons.  The Vela satellites were ...

What causes the diffraction spikes in images of stars?

8 hours ago

When stars are portrayed in media, they are often shown with long spikes emanating from them. Perhaps the most common example is that of the "star of Bethlehem" which, according to the story, led the wise ...

User comments : 8

Adjust slider to filter visible comments by rank

Display comments: newest first

1 / 5 (10) Aug 27, 2014

SUPERNOVA POWER! Chemonuclear Fusion is a type of low energy nuclear fusion that has been shown to produce energy in two experiments. Aneutronic nuclear fusion can provide unlimited electric power without polluting the environment with radioactive waste and greenhouse emissions. Chemonuclear processes in small dense white dwarf stars accelerate the rate of nuclear fusion and cause them to explode in spectacular supernova explosions.

The mission of the Chemonuclear Fusion Project is to raise awareness of this new and vitally important source of environmentally clean energy and to promote research and development.

The Chemonuclear Fusion Project is soliciting volunteers to help our crowdfunding and educational campaigns. Our crowdfunding webpages will soon be up and running. We want people to post to discussion groups and help us get the word out that aneutronic chemonuclear fusion might be the radiation free way to power the world if we can get the funding to build and test reactors.

Artists can help us design T-shirts, mugs, and promotional items to sell and give away to our contributors. Writers to write promotional materials and post to web forums are also wanted. Video producers and professional and amateur scientists who can help the public understand the concepts of chemonuclear fusion are encouraged to contact us also.

Visit our facebook page and give us a like. We welcome your comments and questions!

2 / 5 (8) Aug 27, 2014
If the supernovas exploded millions of years ago why is the interstellar gas still millions of degrees in temperature? Why hasn't it cooled? whats keeping it hot?
5 / 5 (8) Aug 27, 2014
@11791 - The answer's in the same sentence:

"Gas inside the bubble is very thin (0.001 atoms per cubic centimeter) and very hot (roughly a million degrees)—a sharp departure from ordinary interstellar material"

So it's basically insulated, the same way bubbles of vacuum insulate a Thermos flask. There's simply no contact between the hot material and anything cooler to dissipate the heat away..
5 / 5 (4) Aug 27, 2014
"Gas inside the bubble is very thin (0.001 atoms per cubic centimeter) and very hot (roughly a million degrees)—a sharp departure from ordinary interstellar material"

The other point is that radiation at these temperatures depends on density in terms of efficiency. There are no atoms so there is no atomic emission and it's too hot for recombination lines so the most significant radiation source is bremsstrahlung. Bremsstrahlung happens when two charged deflect one another by their electric fields. The important note is there are two particles which have to come very close together so bremsstrahlung is a function of density squared. At very low density it is very inefficient and so this superheated material can last quite a while.
2.3 / 5 (3) Aug 27, 2014
Temperature is a measure of the average speed of particles within a given volume. The term loses its meaning in a vacuum. Each particle has enormous speed (temperature) but there aren't enough particles present to heat a cup of coffee.
1 / 5 (2) Aug 28, 2014
Shitead wrote, "Temperature is a measure of the average speed of particles within a given volume. The term loses its meaning in a vacuum. Each particle has enormous speed (temperature) but there aren't enough particles present to heat a cup of coffee."


Nope. Try vibration. A particle at a million degrees is vibrating quite rapidly. Its temperature isn't altered by its speed through vacuum.
not rated yet Aug 28, 2014
So if I was in a current age space suit floating around outside in this bubble/medium (away from stars) is it going to cook me? Or is there not enough matter in the space around my suit to feel the heat?
1 / 5 (1) Aug 28, 2014
Nope. Try vibration
Nope. Try google.

"The thermodynamic temperature is a measure of the average energy of the translational [SPEED], vibrational, and rotational motions of matter's particle constituents (molecules, atoms, and subatomic particles). The full variety of these kinetic motions, along with potential energies of particles, and also occasionally certain other types of particle energy in equilibrium with these, contribute the total internal energy (loosely, the thermal energy) of a substance... even when a substance is isolated and in thermodynamic equilibrium (all parts are at a uniform temperature and no heat is going into or out of it), the translational motions of individual atoms and molecules occur across a wide range of speeds.." etc