• New models propose alternatives to the standard black hole, challenging the existence of singularities.
• The proposed models include regular black holes and black hole mimickers, each with distinct characteristics and potential observational signatures.
• Future observations, including high-resolution imaging and gravitational wave measurements, may provide evidence to distinguish between these models and the standard black hole.

For over a century, the scientific community has grappled with the concept of singularities at the heart of black holes, predicted by Einstein's theory of general relativity. These singularities, points of infinite density where the laws of physics break down, pose a significant challenge. Recent research, stemming from discussions at an IFPU workshop, explores alternative models that eliminate the singularity, offering new perspectives on the nature of black holes. These models aim to reconcile general relativity with quantum mechanics and provide avenues for observational verification.

• What: The exploration of alternative black hole models that challenge the existence of singularities, including regular black holes and black hole mimickers.
• Who: Researchers collaborating across different groups, including theorists and phenomenologists, with key contributions from Stefano Liberati (SISSA).
• When: The research is based on discussions and findings that have been developed over recent years, with potential future insights from upcoming observational data.
• Where: The research originated from discussions at an IFPU workshop, with theoretical implications for black holes throughout the universe.

The shift away from the singularity model represents a significant development in black hole physics. The 'regular black hole' and 'black hole mimicker' concepts provide testable hypotheses that could bridge the gap between general relativity and quantum mechanics. The reliance on future high-resolution imaging and gravitational wave data underscores the importance of continued investment in astronomical observation technologies. The success of these new models hinges on identifying subtle deviations from the predictions of Einstein's theory, requiring a multidisciplinary approach combining theoretical advancements and observational precision.

Regular black holes, and especially mimickers, are never exactly identical to standard black holes – not even outside the horizon. So observations that probe these regions could, indirectly, tell us something about their internal structure.

We are entering an era where a vast and unexplored landscape is opening up before us.

The exploration of non-singular black hole models marks a pivotal moment in astrophysics. While the standard black hole model with a singularity has been a cornerstone of our understanding, the new proposals offer compelling alternatives that address fundamental theoretical challenges. Future observational data from advanced telescopes and gravitational wave detectors will be crucial in validating or refuting these models, potentially revolutionizing our understanding of gravity and the universe's most enigmatic objects. The field is entering an exciting era of discovery, where the boundaries of knowledge are being pushed.