What can we learn when two black holes tango?

Theoretical astrophysicist Priyamvada Natarajan discusses LIGO’s third gravitational wave detection.

Vocabulary: LIGO detector, black hole, gravitational wave, solar masses, light years, general relativity, angular momentum, binary pair

Next Generation Science Standards: ESS1.A: The Universe and Its Stars, SEP4: Analyzing and Interpreting Data, and CC1: Patterns. Can be used to build towards HS-ESS1–3 and MS-ESS1–3.

Common Core State Standards: CCSS.ELA-LITERACY.RI.6.1, CCSS.ELA-LITERACY.RI.7.1, CCSS.ELA-LITERACY.RI.8.1, CCSS.ELA-LITERACY.RI.9–10.1, CCSS.ELA-LITERACY.RI.11–12.1

An artist’s conception of two merging black holes similar to those detected by LIGO. Credit: LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet)

This week, scientists using the Laser Interferometer Gravitational-Wave Observatory, or LIGO, announced that they had detected another gravitational wave — the third ripple observed since September 2015. The findings were published in the journal Physical Review Letters.

The source of this most recent gravitational wave is a black hole 49 times larger than our sun that was formed by two colliding black holes located 3 billion light-years away. The data indicates that the spin of one or both of the black holes may have a tilted orbit, which can reveal clues to their origins. Theoretical astrophysicist Priyamvada Natarajan explains how this finding sheds light on black hole formation, and how it affects our understanding of general relativity and dark matter.

Audio Excerpt “LIGO Scientists Detect Another Cosmic Collision,” June 2, 2017. (Original Segment)

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Credits: Numerical-relativistic simulation: S. Ossokine, A. Buonanno (Max Planck Institute for Gravitational Physics) and the Simulating eXtreme Spacetimes project; scientific visualization: T. Dietrich (Max Planck Institute for Gravitational Physics), R. Haas (NCSA)

Questions

• Priyamvada Natarajan likens the collision event to a dance, when she talks about “two black holes that are tangoing.” Explain what that analogy is supposed to indicate about these black holes.
• Create a illustrated model that shows the difference between optical light waves and gravitational waves that was confirmed by this third gravitational wave detection.
• The gravitational wave LIGO detected confirmed that the spins of these two black holes were misaligned. Based on that information, how did they end up as a binary pair?
• How will turning on the LIGO arms in India and Italy affect the data available to scientists?
• The third gravitational wave that LIGO detected has confirmed and changed some of our notions about black holes. What is one question about black holes that you think could be answered with LIGO?

Animation of the inspiral and collision of two black holes consistent with the masses and spins of GW170104. (Credit: A. Babul/H. Pfeiffer/CITA/SXS.)

Activity Suggestions

• Introduce students to black holes by using this exploration of black hole formation and density or this series of activities looking at the lifecycle of a star and black holes.
• Engage your students in the science behind LIGO with this series of activities from the LIGO Scientific Collaboration exploring gravitational waves and how the LIGO detector works.

Additional Resources

• The gravitational wave that LIGO detected was the culmination of a century-long search for gravitational waves.
• Hear author Jana Levin talk about some of the scientists who shepherded LIGO on its long journey from thought experiment to reality.