On May 1, 2015, a team of scientists made an incredible prediction: a supernova would occur in the galaxy named SP1149 in November of that year. This was a groundbreaking moment because predicting a supernova is extremely difficult due to their rarity and unpredictability.
A supernova marks the dramatic end of a star’s life, especially for stars that are more than eight times the mass of our sun. When these stars run out of nuclear fuel, they collapse under their own gravity, causing a massive explosion that can shine brighter than entire galaxies. The light from a supernova follows a predictable pattern: it shines brightly for weeks and then fades over several months. However, supernovae are rare; in a galaxy with about 100 billion stars, only around two supernovae might occur every century.
Scientists can estimate how long a star will live based on its mass, brightness, and color temperature, but predicting exactly when a star will explode as a supernova is very uncertain. For example, Betelgeuse, a red supergiant in our Milky Way, is expected to explode within the next few hundred thousand years—a short time in cosmic terms, but a long wait for us.
Despite these challenges, the scientists were granted time on the Hubble Space Telescope to observe SP1149. They started taking images on October 30, 2015. The first two images, taken on October 30 and November 14, showed no supernova. But on December 11, they captured the explosion exactly as predicted.
The success of this prediction was largely due to gravitational lensing. This phenomenon occurs when a massive object, like a galaxy cluster, bends and magnifies the light from a distant source. This effect can create multiple images of the same astronomical event, allowing scientists to see the same supernova in different places.
In this case, the light from the supernova, which exploded 9.3 billion years ago, passed through a galaxy cluster called MACS J1149.5+2223. The cluster’s gravity bent the light, allowing it to reach Earth from multiple paths, making the supernova appear in four different locations.
The images of the supernova appeared at different times because the light took different paths and experienced gravitational time delays. This delay happens because light traveling through curved spacetime seems to move more slowly to an observer. Scientists measured these time delays by studying the supernova’s light curve, which shows how its brightness changes over time.
This discovery was significant because it was the first time a multiply-lensed supernova was observed. While other objects can appear multiple times due to gravitational lensing, they don’t show predictable brightness changes, making this supernova unique.
This discovery has important implications beyond just observing a supernova. One major question in astronomy is the rate at which the universe is expanding, known as the Hubble constant. Traditionally, two methods have been used to measure this constant, but they give different results: about 74 kilometers per second per megaparsec from the distance ladder method and around 67 kilometers per second per megaparsec from cosmic microwave background observations.
The observation of Supernova Refsdal, the first multiply-lensed supernova, offers a new way to measure the Hubble constant. Calculations based on this data suggest a value of 64 kilometers per second per megaparsec, which is closer to the cosmic microwave background measurements than the distance ladder method. This difference has sparked discussions about a potential crisis in cosmology, as the two methods have not yet agreed despite improvements.
The successful prediction and observation of a supernova in galaxy SP1149 highlight the power of modern astronomy and deepen our understanding of the universe’s structure and expansion. The combination of gravitational lensing, time delays, and light curves provides a fascinating look into the complexities of cosmic phenomena, reminding us of the intricate nature of space and time.
Engage in a computer simulation that models the life cycle of a star leading to a supernova. Observe how changes in mass, brightness, and temperature affect the star’s evolution. Discuss with your classmates how these factors contribute to the unpredictability of supernovae.
Conduct a hands-on experiment using lenses to simulate gravitational lensing. Use a light source and a curved glass to observe how light bends and creates multiple images. Relate your observations to how scientists used gravitational lensing to predict the supernova in SP1149.
Analyze real data from a supernova’s light curve. Plot the brightness over time and identify the peak brightness and fading pattern. Discuss how these observations help scientists understand time delays and measure cosmic distances.
Participate in a debate about the different methods of measuring the Hubble constant. Research the distance ladder method and cosmic microwave background observations. Present arguments for which method you believe provides a more accurate measurement and discuss the implications of the differing results.
Create a timeline of the universe’s history, highlighting key events such as the Big Bang, formation of galaxies, and notable supernovae. Include the prediction and observation of the supernova in SP1149. Use this timeline to discuss the significance of supernovae in understanding the universe’s expansion.
Supernova – A supernova is a powerful and luminous explosion of a star, often resulting in the star’s destruction. – The supernova illuminated the surrounding galaxy, providing astronomers with valuable data about stellar life cycles.
Galaxy – A galaxy is a massive system of stars, stellar remnants, interstellar gas, dust, and dark matter, bound together by gravity. – The Milky Way is the galaxy that contains our solar system, and it is just one of billions in the universe.
Gravity – Gravity is the force by which a planet or other celestial body attracts objects toward its center. – The gravity of the black hole was so strong that not even light could escape from it.
Light – Light is electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. – The speed of light in a vacuum is approximately $3 times 10^8$ meters per second, a fundamental constant in physics.
Lensing – Lensing refers to the bending of light rays by gravity, often used to study distant galaxies and dark matter. – Gravitational lensing allowed astronomers to observe a galaxy that would otherwise be hidden behind a massive cluster of stars.
Brightness – Brightness is the perceived intensity of light from a celestial object, often measured in magnitudes. – The brightness of a star can help determine its distance from Earth and its intrinsic luminosity.
Time – Time is a continuous, measurable quantity in which events occur in a sequence, often considered in relation to space in physics. – In Einstein’s theory of relativity, time is intertwined with space, forming the four-dimensional fabric known as spacetime.
Cosmology – Cosmology is the scientific study of the large-scale properties of the universe as a whole. – Modern cosmology seeks to understand the origin, evolution, and eventual fate of the universe.
Expansion – Expansion refers to the increase in distance between parts of the universe over time, as described by the Big Bang theory. – The discovery of the universe’s expansion was a pivotal moment in cosmology, leading to the development of the Big Bang model.
Observation – Observation in astronomy involves collecting data from celestial objects using telescopes and other instruments. – Careful observation of distant stars and galaxies has led to many breakthroughs in our understanding of the universe.
