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SIDM Solves the Final Parsec Problem
Context: A recent study by Scientists from Canada suggests that self-interacting dark matter could solve the final parsec problem in supermassive black hole mergers.
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The study proposes that (Self-Interacting Dark Matter) SIDM could address the final parsec problem and also explain the gravitational wave spectrum observed by Pulsar Timing Array collaborations in 2021.
The Final Parsec Problem
- When two galaxies merge, their SMBHs also begin to merge. However, the merger stalls when the black holes are around 1 parsec (approximately 30.9 trillion kilometres) apart.
- Gravitational waves drive the SMBHs inward, but dynamical friction (drag from surrounding matter) slows their approach.
Key Highlights:
- Dark matter is mostly found in the galactic halo, surrounding the visible galaxy, and also near the galactic core where SMBHs reside. Its presence in these regions is crucial for the SMBH merger process.
- Researchers calculated dark matter density profiles around SMBHs for both SIDM and cold dark matter (CDM).
- Analysed dynamical friction effects, and simulated gravitational wave spectra under various dark matter scenarios.
- The optimal cross-sectional area is between 2.5 and 25 cm²/g (for every gram of dark matter, the effective interaction area should fall within this range).
- The interactions between SIDM particles are influenced by their relative velocity, which is affected by the mass of the unknown force carrier or mediator.
- It is expected if the mediator’s mass is roughly 1% of the dark matter particle mass.
- The velocity of SIDM particles required for optimal interactions is estimated to be between 300 and 600 km/s.
Dark Matter & Dark Energy
- Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects.
- It constitutes about 28% to 32% of the universe’s total mass-energy content. The evidence arises from various astrophysical observations, including Galactic Rotation Curves, and Gravitational Lensing.
- Dark energy is an even more enigmatic component, accounting for approximately 68% to 72% of the universe’s energy density.
- It is thought to be responsible for the accelerated expansion of the universe. This led to various hypotheses, including the Cosmological Constant, and Quintessence.
About Self-Interacting Dark Matter (SIDM):
- It is a hypothetical form of dark matter where particles interact through a previously unknown force.
- Interaction Effects: The interactions between SIDM particles can alter the density and velocity profiles of dark matter in a galaxy.
- SIDM interactions can lead to a more efficient funnelling of matter and energy toward the SMBH.
- Influencing dark matter density and distribution may reduce the dynamic friction that stalls the SMBH merger, thus aiding the merging process.
Implications:
- Dark Matter Constraints: It provides a new way to probe dark matter in the innermost regions of galaxies.
- Team developing numerical simulations to better understand how dark matter profiles react to the energy injected by merging black holes.
International Pulsar Timing Array (IPTA)
- It is a collaborative effort consisting of the European Pulsar Timing Array (EPTA), North American Nanohertz Observatory for Gravitational Waves (NANOGrav), Indian Pulsar Timing Array Project (InPTA), Parkes Pulsar Timing Array (PPTA).
- Objective: To detect and analyse low-frequency gravitational waves using a global network of approximately 100 millisecond pulsars.
- Unlike ground-based detectors like LIGO and VIRGO, which measure the time-of-flight of laser beams in interferometers, the IPTA measures the time-of-flight of electromagnetic pulses from pulsars.
- It focuses on supermassive black hole binaries, which are billions of solar masses and exist at the centres of galaxies.