In June 2016, scientists from the LIGO collaboration announced the second detection of gravitational waves. Which of the following statements about this event is or are correct?

Introduction / Context:

This question relates to modern physics and astronomy, focusing on the historic detection of gravitational waves by the LIGO observatories. Gravitational waves are ripples in spacetime predicted by Einstein general theory of relativity. In June 2016, the LIGO team reported a second confirmed detection. The question asks which given statements correctly describe that particular event.

Given Data / Assumptions:

• Statement 1: In June 2016, the LIGO group announced the detection of a second set of gravitational waves.
• Statement 2: The waves were generated due to the merger of two black holes located about 1.4 billion light years away.
• Statement 3: The waves were produced by the collision of two white dwarf stars at about 1.4 billion light years distance.
• The task is to determine which combination of these statements is correct.

Concept / Approach:

The early confirmed detections by LIGO all involved mergers of stellar mass black holes, not white dwarf stars or neutron stars. The second announced event, often labelled GW151226, was interpreted as originating from the merger of two black holes several times the mass of the Sun, at a distance of roughly 1.4 billion light years. Therefore, statements mentioning black hole mergers and the June 2016 announcement are correct, while any reference to white dwarf collisions is inaccurate in this context.

Step-by-Step Solution:

Verification / Alternative check:

Summaries of the GW151226 event explain that the detected signal matched the inspiral and merger of two black holes with masses roughly several solar masses. There is no mention of white dwarf stars for this detection. White dwarf mergers are possible astrophysical events but were not involved in the second published gravitational wave observation by LIGO. Hence, matching the date, distance and source type confirms that statements 1 and 2 are correct together.

Why Other Options Are Wrong:

The option 1 only ignores the correct information provided in statement 2 about the black hole merger and its distance. The combination 2 and 3 only is incorrect because statement 3 contradicts the documented source type. The option 1, 2 and 3 wrongly includes the white dwarf statement, which is not supported by evidence. The option 3 only accepts the entirely wrong description and therefore cannot be chosen. Only the combination 1 and 2 captures the accurate description of the event.

Common Pitfalls:

Students may confuse different astrophysical events such as black hole mergers, white dwarf collisions and neutron star mergers. Another pitfall is to assume that any pair of massive stars could generate similar gravitational waves in early detections, leading to acceptance of the white dwarf statement. Reading questions carefully and associating specific LIGO announcements with their correct sources helps avoid such confusion.

Final Answer:

The correct combination of statements about the June 2016 LIGO event is 1 and 2 only.