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Supernovas & Remnants

Supernovas are some of the brightest events in the universe, occasionally outshining entire galaxies at their peak. Many supernovas can be seen from billions of light-years away, and nearby supernovas in past centuries have been visible during the daytime. Today, astronomers distinguish two types of supernova: those involving white dwarfs, and those that are the explosions of very massive stars. Both types are responsible for creating and spreading new elements through space, which are the chemical building blocks for the next generation of stars and planets.

Our Work

Center for Astrophysics | Harvard & Smithsonian astronomers use many tools to understand supernovas and their remnants:

  • Studying the varieties of core-collapse supernovas to learn about their similarities and differences. In particular, a rare type known as a “superluminous” supernova may occur in environments rich in heavier elements that astronomers call “metals”. However, it’s uncertain if all such supernovas happen that way.
    Astronomers Discover ‘Heavy Metal’ Supernova Rocking Out

  • Monitoring the closest supernova of recent years: the explosion known as Supernova 1987A. This supernova was the explosion of a very massive blue star in a neighboring galaxy, the Large Magellanic Cloud. Its relative closeness to the Milky Way has let astronomers track the remnant using NASA’s Chandra X-ray Observatory, the Hubble Space Telescope, and other instruments. They have learned the remnant has some mysterious features that make Supernova 1987A unique.
    The Dawn of a New Era for Supernova 1987A

  • Observing Type Ia supernovas and their remnants to determine exactly what the original system contained before the explosion. Specifically, we still don’t know if Type Ia supernovas involve two white dwarfs or a white dwarf in a binary with an ordinary star — or if the supernovas we see represent both types of progenitor systems.
    First Discovery of a Binary Companion for a Type Ia Supernova

  • Studying supernova remnants in multiple kinds of light, to reconstruct their interiors and the processes shaping them. Astronomers use the Chandra X-ray Observatory, the CfA’s Very Energetic Radiation Imaging Telescope Array System (VERITAS), and other instruments to trace the high energy collisions, magnetic fields, and shock waves inside remnants. That includes studies of Tycho’s Supernova, a nearby explosion observed by Tycho Brahe in 1572, which we now know was a Type Ia supernova. This remnant’s nearness to us, along with its relative recency, means we have a lot of excellent data on the system.
    Tycho's Supernova Remnant: Chandra Movie Captures Expanding Debris From a Stellar Explosion

  • Modeling supernovas using computer simulations, to understand the ways they explode. These studies are particularly important for tracking the creation of new elements, but also for identifying the sources of unusual supernovas. Scientists suspect the bright transient sources known as long-duration gamma ray bursts are energetic supernovas, and theoretical work has helped cement that connection.
    The Gamma Ray Burst – Supernova Connection

This NASA's Chandra X-ray Observatory image shows glowing material in the Cassiopeia A supernova remnant. The explosions of giant stars seed the cosmos with new chemical elements, providing the raw materials for future stars and planets.

Credit: NASA/CXC/SAO

Explosions in the Sky

In the year 1054 CE, observers around the world recorded a new “star” in the sky, which was briefly bright enough to be seen in the daytime, before fading to invisibility. With the advent of telescopes, astronomers connected this with a strangely shaped cloud of gas they named the Crab Nebula. Today, we recognize the “star” was a supernova, and the Crab Nebula is the supernova remnant.

Supernova explosions come in two distinct flavors:

  • Type Ia supernovas — pronounced “type one a” — involve white dwarfs, which explode if they exceed a maximum mass about 1.4 times the mass of the Sun, known as the Chandrasekhar limit. This can happen either when enough material is dumped on a white dwarf to push it past the Chandrasekhar limit, or when two white dwarfs collide and their combination exceeds the maximum. Because all white dwarfs are subject to the Chandrasekhar limit, Type Ia supernovas explode in very similar ways. That gives the light they produce specific patterns, which means they can be used as cosmic distance markers.

  • Core-collapse supernovas are the explosions of stars greater than 8 times the mass of the Sun. These stars fuse increasingly heavy elements in their core until they reach iron. Beyond that, it takes more energy to keep fusion going than the star can manage, so the core collapses, while the outer layers of the star explode outward. Core-collapse supernovas are very different from each other, since the stars that produce them are diverse. The cores of the most massive stars collapse into black holes, while the middle range of masses leave behind neutron stars.

All types of supernovas produce new elements thanks to fusion during the explosion. Much of the iron in the universe comes from Type Ia supernovas, while many heavier elements came from core-collapse supernovas. The outflow of material from the explosions enriches interstellar space, providing the raw materials for new stars and planets. Many of the ingredients that made Earth — including life — came from supernovas.

The Supernova Group at the Center for Astrophysics | Harvard & Smithsonian has cataloged thousands of supernova “light curves”: the increase and decrease of light emission during and after the explosion. These light curves are helpful for identifying the atoms and molecules present in the supernova, measuring the distance to the supernova, and determining what kind of supernova exploded in the first place. https://www.cfa.harvard.edu/supernova/

 

What’s Left Behind

Supernova explosions are dramatic, but the leftovers are just as interesting from a scientific point of view. These supernova remnants — including the Crab Nebula — contain information about the original system that exploded. They are also hotbeds of activity, containing powerful magnetic fields and hot plasma that can create shock waves in the surrounding material. As a result, supernova remnants are extremely important for understanding the life cycle of stars and physical processes in extreme environments.

With Type Ia supernovas, the exploding stars are completely destroyed. In the case of core-collapse supernovas, however, the remnant also harbors the neutron star or black hole created from the core of the dead star. For example, the Crab Nebula harbors a pulsar, a spinning neutron star that interacts with materials in the supernova remnant. In particular, it creates a disk of hot matter around it and a powerful jet shooting away, which heats up matter around it.