The fact
While I’ve heard about supernovae before, I’ve never got to see one, let alone take a photo of one.
It was surreal. Here I was, in the Wairarapa Dark Sky Reserve at night, frantically trying to focus the camera while racing to take the pic before moonrise. Whilst I was rushing, the supernova had already happened some twenty-two million years ago, bringing death and destruction to its corner of the galaxy NGC 3621.
How many worlds would have been bathed in lethal radiation by its blast? We will never know. How many new lives would have catalyzed, we will also never know. We exist only because of past supernovae that happened a long time ago in our corner of the Milky Way – the oxygen we breathe right now comes from them. What a strange reminder of how lucky we are to be alive.
I looked at this supernova SN2024ggi last night on the screen of my camera in silence, in the dark, with a morepork by my side, and it was out of this world.
Hari
Technical Insights into SN 2024ggi
Supernova SN 2024ggi occurred on a Friday (the 12th of April 2024) in the spiral galaxy NGC 3621, located about 22 million light-years away in the constellation Hydra. This type of supernova is known as Type II – core collapse. When a massive star runs out of nuclear fuel, it collapses under its own gravity. This is the end of the star, which blows itself apart, throwing the star’s material into space and enriching the interstellar medium with heavy elements like iron, carbon, and oxygen. These elements are what life as we know it is made of.
The light from this supernova travelled 22 million years to reach us, providing a snapshot of the history of our universe. Looking at it, we can literally see a bright starlight in a place where just a day before, there seemed to have been none. The blast from the supernova outshines its host galaxy. Here on Earth, we can see a star-like object that is no different from the stars surrounding it in our galaxy.
Astrobiology and the Origin of Elements
The death of massive stars in supernova explosions is one of the primary ways the universe creates, recycles and redistributes materials. The elements produced in these cataclysmic events are necessary for forming new stars, planets, and, perhaps, life. This natural cycle of stellar evolution is directly linked to how our life appeared and evolved on Earth.
Oxygen, essential for life on our planet together with other life-supporting elements, originates from supernovae. Understanding the life cycle of stars not only explains the origins of elements but also provides insights into the potential habitability of other worlds—a key topic in astrobiology.
Back to Earth, in New Zealand
In the New Zealand curriculum, the life cycle of a star is covered in the science learning area.
The content related to stars, including their life cycle, is typically introduced at Level 5. (This level generally corresponds to students in Year 9 and Year 10, the first two years of secondary education in New Zealand.) The curriculum focuses on giving students an understanding of astronomical systems and includes exploring how stars like our Sun produce energy. The New Zealand curriculum also integrates the concepts of stars and their life cycles in broader themes like Earth and Space Science at Level 8, typically for students in Year 12 and Year 13. This higher level includes deeper discussions on astrophysics, encompassing stellar evolution processes, the different types of stars, and their end stages, such as supernovae (NZ Curriculum Online).
So, having a supernova occurring right now is a great opportunity to revisit these topics.
Questions we pondered about
Seeing such a rare event does raise many questions. Here is a small series of what one might possibly ask themselves or ask an astrophysicist for a change. Our astrophysicist in residence is Sam, so we asked him the following questions.
What would have happened to that part of the galaxy in which this supernova exploded?
When a supernova like SN 2024ggi explodes, it dramatically impacts its surrounding environment in the galaxy. Here are the things that would have happened in the process:
An enormous amount of energy and radiation was released
The initial explosion releases tremendous energy and radiation, outshining the rest of the galaxy for a brief period. This radiation can be lethal for any planetary systems close to the supernova, potentially stripping away atmospheres or causing significant biological damage to any life forms (for life as we know it).
Stellar material was ejected into space
Supernovae eject vast amounts of stellar material into space at speeds of up to tens of thousands of kilometres per second. This material includes heavy elements such as iron, carbon, and oxygen, which were synthesized in the core of the star during its life and in the explosive supernova event itself.
A shock wave followed.
The ejected material forms a shock wave that travels through the surrounding interstellar medium. This shock wave can compress nearby gas clouds, potentially triggering the formation of new stars. This process is known as “triggered star formation.”
The interstellar medium got enriched with heavier elements (that is, heavier than hydrogen and helium)
The materials ejected by the supernova mix with the interstellar medium, enriching it with heavier elements. This enrichment is crucial for the chemical evolution of the galaxy, as these elements are the building blocks for new stars, planets, and potentially life. Over time, these materials can be incorporated into new star systems.
Nebulae (stellar clouds) formed.
The remnants of the supernova explosion can form a nebula, an expanding shell of gas and dust. The Crab Nebula, for example, is the remnant of a supernova observed in 1054 AD. These nebulae can be observed for thousands of years as they expand and slowly blend with the surrounding interstellar medium. While we cannot observe the nebula for SN2024ggi, we have plenty of observable examples in our own galaxy. We try and look at these as much as we can every night at Star Safari.
A Neutron Star, or maybe even a Black Hole, is what was left of the star that exploded.
Depending on the mass of the original star, the core left behind by a supernova can become a neutron star or a black hole. These compact objects can have further interactions with their environment, such as emitting strong jets of particles or forming binary systems that produce gravitational waves.
Thus, a supernova like SN 2024ggi not only marks the end of the life of its star but also contributes to the cycle of birth and death in its galaxy, playing a vital role in the evolution of the cosmos.
How often do supernovae occur? In our galaxy or somewhere else.
Supernovae are relatively rare events, but when considering the vastness of the universe, they occur regularly across different galaxies.
Frequency of Supernovae:
- In Our Galaxy (The Milky Way): Supernovae in the Milky Way are estimated to occur about once every 50 years on average. However, this is an average figure; the observed rate can vary widely. Due to dust and gas obscuring our view, many supernovae in the Milky Way might go unnoticed.
- In Other Galaxies: Supernovae can occur more frequently in other galaxies, especially those actively forming stars. Some estimates suggest that a typical galaxy might experience a supernova event once every 100 years or so. However, this rate can be much higher in starburst galaxies where intense star formation is taking place.
When was the last supernova observed in our galaxy?
Recent Supernovae Observations:
The last supernova observed near our galaxy, the Milky Way, was SN 1987A, which actually occurred in one of the Milky Way’s satellite galaxies, the Large Magellanic Cloud, in 1987. This was one of the closest and brightest supernovae observed in recent times, providing valuable data to astronomers.
Albert Jones (https://en.wikipedia.org/wiki/SN_1987A) was a New Zealand astronomer who co-discovered this supernova. He lived in Nelson and observed it with his homemade telescope.
Stamps produced by New Zealand Post, for which Hari wrote the commentaries and intro. New Zealand Space Pioneers
In Our Galaxy: We had a supernova in 1604, in the constellation Ophiuchus, observed by Johannes Kepler, before that there was the supernova of 1572 observed by Tycho Brahe in Cassiopeia and the supernova that now has left the Crab Nebula in Taurus, observed by the Chinese in 1054.
When was the last supernova observed in another galaxy?
In Another Galaxy: Supernovae in other galaxies are observed much more frequently, thanks to modern telescopes that monitor large swaths of the sky. For example, SN 2024ggi in galaxy NGC 3621 is a recent instance. Another recent example is SN 2021hiz in the galaxy NGC 3147, observed in 2021. With current technology, astronomers can detect supernovae in distant galaxies several times a month.
What is the impact of a supernova explosion?
When a supernova happens, if there are any planets with life, what would happen to them? For example, we have a star named Betelgeuse in our galaxy that we know is nearing the end of its life. Will anything happen to Earth if Betelgeuse explodes? What is the radius of physical destruction and the radius of lethal radiation?
The impact of a supernova on nearby planets, particularly those with life, depends on the distance of the planets from the supernova. Here are the important aspects of supernova effects on planetary systems:
Physical destruction:
The actual physical destruction caused by a supernova, such as the shockwave that might disrupt a planetary system, generally affects the region within a few light-years from the explosion. The intense blast wave can strip away planetary atmospheres and even eject planets from their orbits, but this generally occurs only if the planets are very close to the supernova.
Radiation impact:
More extensive than the shockwave is the effect of intense radiation, which can be harmful over much greater distances. Supernovae emit a burst of radiation across the electromagnetic spectrum, including lethal doses of gamma rays and X-rays. This radiation can cause significant biological damage and potentially lead to mass extinctions. The deadly radius for significant biological damage can extend to about 30 light-years from the supernova. This radiation can also deplete ozone layers in planetary atmospheres, increasing exposure to harmful solar ultraviolet (UV) rays for hundreds or thousands of years after the supernova occurs.
For example, Betelgeuse – our next waiting to happen supernova
Betelgeuse is a well-known red supergiant star in the Orion constellation, and it’s expected to go supernova sometime in the next 10,000 years—a blink of an eye in cosmological terms, but not necessarily soon on a human timescale. It’s approximately 642 light-years away from Earth. If Betelgeuse were to explode today:
- Physical effects: Earth would not experience any physical destruction from the shockwave, as we are far outside the range where such effects would be significant.
- Radiation effects: The distance dramatically reduces the impact of any radiation. While Betelgeuse’s supernova would be an incredibly bright event in the sky, potentially visible even during the day, it is too far away to pose a threat of harmful radiation effects to Earth. If directed precisely towards Earth, the gamma-ray burst could have a measurable but minor impact on the upper atmosphere, but it wouldn’t be catastrophic.
Read here more about Betelgeuse in an article written by Sam on Milky-Way.Kiwi
General safety distance for a supernova explosion
While a supernova needs to be closer than about 30 light-years to pose a significant radiation hazard, no stars within this danger zone to Earth are currently known. Thus, while supernovae are powerful and potentially dangerous, the vast distances involved generally shield planets, including Earth, from the worst effects unless they are relatively close to the explosion.
