Supernova Signatures on Life in the Local Bubble

Winds from a central massive hot star cause the expansion of interstellar material, blowing outwards to create the Bubble Nebula. Credit: NASA, ESA, Hubble Heritage Team; CC BY 4.0

As the solar system travels through the Milky Way, our planet and the life it harbors are exposed to a variety of environments. A recent study suggests that a nearby supernova may have played a role in the evolution of life on Earth

The Local Bubble

About 6 million years ago, the solar system wandered into a 1,000 light-year-wide void known as the Local Bubble. Winds from massive stars and ionizing radiation from an estimated 15 supernovae carved out this bubble over the last 15 million years. As the solar system traveled from the bubble’s edge to its current position in the center, at least nine of the bubble-sculpting supernovae exploded, showering the Earth with supernova byproducts and intense radiation.

Evidence of these past explosions is embedded within the Earth’s crust — radioactive isotopes formed only in supernovae have decayed over time in deep-sea sediments. Less conspicuous are the ways cosmic rays from supernovae may have impacted the Earth; high-energy charged particles rained into the solar system, exposing the planet and the life on it to powerful radiation. Studying the Local Bubble and tracing the history of supernova explosions within it will allow researchers to gauge how the local environment has impacted our planet and the life it harbors.

Map of the Local Bubble showing the locations of surrounding stellar associations. The solar system lies near the center of the Local Bubble, and the surrounding stellar associations hosted supernovae that blew up the bubble. Modified from Nojiri et al 2025

Modeling Nearby Supernovae and Cosmic Radiation

Starting with the decay rate of the deep-sea isotopes, scientists estimate peaks in radioactive iron deposits approximately 2–3 and 5–6 million years ago. Using this information and the recent mapping of stellar associations in the Local Bubble, Caitlyn Nojiri (University of California, Santa Cruz) and collaborators modeled the necessary supernova input to produce the level of radioactive material present on Earth. From their modeling, they estimate that the iron peak ~2.5 million years ago can be attributed to a single supernova explosion from either the Upper Centaurus Lupus or Tucana Horologium stellar associations. The iron peak 5–6 million years ago, the authors suggest, arises from the solar system passing through the enriched outer shell of the Local Bubble.

Given the amount of radioactive iron deposited on Earth, the authors predict a powerful supernova progenitor capable of releasing some of the highest-energy cosmic rays in the universe. Through knowing the approximate location of the supernova and modeling its energy output, the authors estimate the amount of cosmic radiation Earth was exposed to from the time the supernova exploded to now. In their model, cosmic-ray radiation varies over time as the supernova evolves, meaning the Earth received a much higher volume of cosmic rays for the first 100,000 years after the explosion.

Cosmic-ray spectra (top panel) and the amount of cosmic radiation received at various depths on Earth (bottom panel) for the modeled supernova in the Upper Centaurus Lupus stellar association. Modified from Nojiri et al 2025

Impacts on Life

What does this cosmic-ray exposure mean for life on Earth? Though the exact effects of this radiation are not certain, biological studies have shown that radiation exposure can cause DNA to break, which can accelerate the rate at which genetic mutations and evolutionary changes occur. The authors note a prior study that showed the rate of virus diversification in Lake Tanganyika in Africa accelerated 2–3 million years ago. Though this cannot be definitively attributed to the supernova, the overlapping timeframes are suggestive of cosmic radiation playing a role in the evolution of life on our planet.

This study underscores the importance of considering cosmic radiation when it comes to understanding the environmental factors that drove biological evolution on Earth. Further studies must be performed in order to constrain the threshold at which this radiation goes from driving species diversification to becoming detrimental to life and its evolution. The Local Bubble has left imprints on the solar system and on Earth in ways that astronomers and biologists will continue to uncover.

By Lexi Gault

Citation

“Life in the Bubble: How a Nearby Supernova Left Ephemeral Footprints on the Cosmic-Ray Spectrum and Indelible Imprints on Life,” Caitlyn Nojiri et al 2025 ApJL 979 L18. doi: 10.3847/2041-8213/ada27a

Source: American Astronomical Society/AAS-Nova

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NASA Is Taking a New Look at Searching for Life Beyond Earth

A zoom into the Hubble Space Telescope photograph of an enormous, balloon-like bubble being blown into space by a super-hot, massive star. Astronomers trained the iconic telescope on this colorful feature, called the Bubble Nebula, or NGC 7635. Credits: NASA, ESA, and the Hubble Heritage Team (STScI/AURA), F. Summers, G. Bacon, Z. Levay, and L. Frattare (Viz 3D Team, STScI)

Since the beginning of civilization, humanity has wondered whether we are alone in the universe. As NASA has explored our solar system and beyond, it has developed increasingly sophisticated tools to address this fundamental question. Within our solar system, NASA’s missions have searched for signs of both ancient and current life, especially on Mars and soon, Jupiter’s moon Europa. Beyond our solar system, missions, such as Kepler and TESS, are revealing thousands of planets orbiting other stars. 

The explosion of knowledge of planets orbiting other stars, called exoplanets, and the results of decades of research on signatures of life - what scientists call biosignatures - have encouraged NASA to address, in a scientifically rigorous way, whether humanity is alone. Beyond searching for evidence of just microbial life, NASA now is exploring ways to search for life advanced enough to create technology.

Technosignatures are signs or signals, which if observed, would allow us to infer the existence of technological life elsewhere in the universe. The best known technosignature are radio signals, but there are many others that have not been explored fully. 

In April 2018, new interest arose in Congress for NASA to begin supporting the scientific search for technosignatures as part of the agency’s search for life. As part of that effort, the agency is hosting the NASA Technosignatures Workshop in Houston on Sept. 26-28, 2018, with the purpose of assessing the current state of the field, the most promising avenues of research in technosignatures and where investments could be made to advance the science. A major goal is to identify how NASA could best support this endeavor through partnerships with private and philanthropic organizations. 

To view the workshop online, visit: http://www.ustream.tv/channel/asteroid-initiative-idea-synthesis---3

On Thursday, Sept. 27 at 1 p.m. EDT, several of the workshop’s speakers will be answering questions in a Reddit AMA.

 What are Technosignatures? 

The term technosignatures has a broader meaning than the historically used “search for extraterrestrial intelligence,” or SETI, which has generally been limited to communication signals. Technosignatures like radio or laser emissions, signs of massive structures or an atmosphere full of pollutants could imply intelligence. 

In recent decades, the private and philanthropic sectors have carried out this research. They have used such methods as searching for patterns in low-band radio frequencies using radio telescopes. Indeed, humanity's own radio and television broadcasts have been drifting into space for a number of years. 

NASA’s SETI program was ended in 1993 after Congress, operating under a budget deficit and decreased political support, cancelled funding for a high-resolution microwave survey of the skies. Since then, NASA’s efforts have been directed towards furthering our fundamental understanding of life itself, its origins and the habitability of other bodies in our solar system and galaxy. 

History of the Search for Technological Life 

Efforts to detect technologically advanced life predates the space age as early 20th century radio pioneers first foresaw the possibility of interplanetary communication. Theoretical work postulating the possibility of carrying signals on radio and microwave bands across vast distances in the galaxy with little interference led to first “listening” experiments in the 1960s. 

Thanks to NASA’s Kepler mission’s discovery of thousands of planets beyond our solar system,including some with key similarities to Earth, it’s now possible to not just imagine the science fiction of finding life on other worlds, but to one day scientifically prove life exists beyond our solar system. 

As NASA's 2015 Astrobiology Strategy states: "Complex life may evolve into cognitive systems that can employ technology in ways that may be observable. Nobody knows the probability, but we know that it is not zero.” As we consider the environments of other planets, “technosignatures” could be included in the possible interpretations of data we get from other worlds. 

Debate about the probability of finding signals of advanced life varies widely. In 1961, astronomer Frank Drake created a formula estimating the number of potential intelligent civilizations in the galaxy, called the Drake equation, and calculated an answer of 10,000. Most of the variables in the equation continue to be rough estimates, subject to uncertainties. Another famous speculation on the subject called the Fermi paradox, posited by Italian physicist Enrico Fermi, asserted that if another intelligent life form was indeed out there, we would have met it by now. 

NASA’s SETI work began with a 1971 proposal by biomedical researcher John Billingham at NASA’s Ames Research Center for a 1,000-dish array of 100-meter telescopes that could pick up television and radio signals from other stars. “Project Cyclops” was not funded, but in 1976, Ames established a SETI branch to continue research in this area. NASA’s Jet Propulsion Laboratory (JPL) also began SETI work. 

In 1988, NASA Headquarters in Washington formally endorsed the SETI program leading to development of the High Resolution Microwave Survey. Announced on Columbus Day in 1992 - 500 years after Columbus landed in North America - this 10-year, $100 million project included a targeted search of stars led by Ames using the 300-meter radio telescope in Arecibo, Puerto Rico, and an all-sky survey led by JPL using its Deep Space Network dish. The program lasted only a year before political opposition eliminated the project and effectively ended NASA’s research efforts in SETI. 

Why Start Looking at Technosignatures Now?

Fueled by the discovery that our galaxy is teeming with planets, interest in detecting signs of technologically-advanced life is again bubbling up. Kepler’s discovery in 2015 of irregular fluctuations in brightness in what came to be known as Tabby’s Star led to speculation of an alien megastructure, though scientists have since concluded that a dust cloud is the likely cause. However, Tabby’s Star has demonstrated the potential usefulness of looking for anomalies in data collected from space, as signs of technologically-advanced life may appear as aberrations from the norm. 

Scientists caution that we will need more than an unexplained signal to definitively prove the existence of technological life. For example, there can be a lot of radio frequency interference from Earth-based sources.

NASA will continue assessing promising current efforts of research in technosignatures and investigating where investments could be made to advance the science. Although we have yet to find signs of extraterrestrial life, NASA is amplifying exploring the solar system and beyond to help humanity answer whether we are alone in the universe. 

From studying water on Mars, probing promising “oceans worlds” such as Europa or Saturn’s moon Enceladus, to looking for biosignatures in the atmospheres of exoplanets, NASA’s science missions are working together with a goal to find unmistakable signs of life beyond Earth. And perhaps that life could indeed be more technologically advanced than our own.

Fascinating.

Editor: Tricia Talbert

Source: NASA/Solar System and Beyond

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Hubble Sees a Star 'Inflating' a Giant Bubble

Bubble Nebula (NGC 7635)

Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Ground-based Field of View and Location of the Bubble Nebula

This graphic shows the wider context of the Bubble Nebula. The National Optical Astronomy Observatory (NOAO) image (left) by Travis Rector has been rotated and cropped to be north-up and closer to the orientation of the Hubble Space Telescope image (right). In addition to the inner bubble seen in the Hubble image, the wider view shows a large cloud complex, including two larger shells surrounding the massive star near the center.  Credit: T. Rector/University of Alaska Anchorage, H. Schweiker/WIYN and NOAO/AURA/NSF, NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Release images -  Release Videos

Twenty-six candles grace NASA's Hubble Space Telescope's birthday cake this year, and now one giant space "balloon" will add to the festivities. Just in time for the 26th anniversary of Hubble's launch on April 24, 1990, the telescope has photographed an enormous, balloon-like bubble being blown into space by a super-hot, massive star. Astronomers trained the iconic telescope on this colorful feature, called the Bubble Nebula, or NGC 7635. The bubble is 7 light-years across — about one-and-a-half times the distance from our sun to its nearest stellar neighbor, Alpha Centauri. The Bubble Nebula lies 7,100 light-years from Earth in the constellation Cassiopeia.

For the 26th birthday of NASA's Hubble Space Telescope, astronomers are highlighting a Hubble image of an enormous bubble being blown into space by a super-hot, massive star. The Hubble image of the Bubble Nebula, or NGC 7635, was chosen to mark the 26th anniversary of the launch of Hubble into Earth orbit by the STS-31 space shuttle crew on April 24, 1990.

"As Hubble makes its 26th revolution around our home star, the sun, we celebrate the event with a spectacular image of a dynamic and exciting interaction of a young star with its environment. The view of the Bubble Nebula, crafted from Wide Field Camera 3 images, reminds us that Hubble gives us a front-row seat to the awe-inspiring universe we live in,” said John Grunsfeld, astronaut and associate administrator of NASA's Science Mission Directorate at NASA Headquarters, in Washington, D.C.

The Bubble Nebula is 7 light-years across — about one-and-a-half times the distance from our sun to its nearest stellar neighbor, Alpha Centauri — and resides 7,100 light-years from Earth in the constellation Cassiopeia.

The seething star forming this nebula is 45 times more massive than our sun. Gas on the star gets so hot that it escapes away into space as a "stellar wind" moving at over 4 million miles per hour. This outflow sweeps up the cold, interstellar gas in front of it, forming the outer edge of the bubble much like a snowplow piles up snow in front of it as it moves forward.

As the surface of the bubble's shell expands outward, it slams into dense regions of cold gas on one side of the bubble. This asymmetry makes the star appear dramatically off-center from the bubble, with its location in the 10 o'clock position in the Hubble view.

Dense pillars of cool hydrogen gas laced with dust appear at the upper left of the picture, and more "fingers" can be seen nearly face-on, behind the translucent bubble.

The gases heated to varying temperatures emit different colors: oxygen is hot enough to emit blue light in the bubble near the star, while the cooler pillars are yellow from the combined light of hydrogen and nitrogen. The pillars are similar to the iconic columns in the "Pillars of Creation" in the Eagle Nebula. As seen with the structures in the Eagle Nebula, the Bubble Nebula pillars are being illuminated by the strong ultraviolet radiation from the brilliant star inside the bubble.

The Bubble Nebula was discovered in 1787 by William Herschel, a prominent British astronomer. It is being formed by a prototypical Wolf-Rayet star, BD +60°2522, an extremely bright, massive, and short-lived star that has lost most of its outer hydrogen and is now fusing helium into heavier elements. The star is about 4 million years old, and in 10 million to 20 million years, it will likely detonate as a supernova.

Hubble's Wide Field Camera 3 imaged the nebula in visible light with unprecedented clarity in February 2016. The colors correspond to blue for oxygen, green for hydrogen, and red for nitrogen. This information will help astronomers understand the geometry and dynamics of this complex system.

The Bubble Nebula is one of only a handful of astronomical objects that have been observed with several different instruments onboard Hubble. Hubble also imaged it with the Wide Field Planetary Camera (WFPC) in September of 1992, and with Wide Field Planetary Camera 2 (WFPC2) in April of 1999.

For more information, contact:

Felicia Chou
NASA Headquarters, Washington, D.C.
202-358-0257
felicia.chou@nasa.gov

Ann Jenkins / Ray Villard
Space Telescope Science Institute, Baltimore, Maryland
410-338-4488 / 410-338-4514
jenkins@stsci.edu / villard@stsci.edu

Zolt Levay
Space Telescope Science Institute, Baltimore, Maryland
410-338-4907
levay@stsci.edu

Source: HubbleSite

Hubble shears a "woolly" galaxy

 NGC 3521
Credit: ESA/Hubble & NASA and S. Smartt (Queen's University Belfast)
Acknowledgement: Robert Gendler

This new image of the spiral galaxy NGC 3521 from the NASA/ESA Hubble Space Telescope is not out of focus. Instead, the galaxy itself has a soft, woolly appearance as it a member of a class of galaxies known as flocculent spirals.

Like other flocculent galaxies, NGC 3521 lacks the clearly defined, arcing structure to its spiral arms that shows up in galaxies such as Messier 101, which are called grand design spirals. In flocculent spirals, fluffy patches of stars and dust show up here and there throughout their discs. Sometimes the tufts of stars are arranged in a generally spiralling form, as with NGC 3521, but illuminated star-filled regions can also appear as short or discontinuous spiral arms.

About 30 percent of galaxies share NGC 3521's patchiness, while approximately 10 percent have their star-forming regions wound into grand design spirals.

NGC 3521 is located almost 40 million light-years away in the constellation of Leo (The Lion). The British astronomer William Herschel discovered the object in 1784. Through backyard telescopes, NGC 3521 can have a glowing, rounded appearance, giving rise to its nickname, the Bubble Galaxy.

Source: ESA/Hubble - Space Telescope