Gravitational dance between massive bodies, tidal forces occur because the attraction of gravity from an object depends on your distance from it. For example, the side of the Earth near the Moon is drawn a little more than the side opposite the Moon. As a result, the Earth stretches and flattens a bit. On Earth, this effect is subtle but strong enough to give the oceans tides. However, near a black hole, tidal forces can be much stronger, creating an effect known as spaghetti.
The strength of the tidal force depends on the mass of an object and how close you are to it. The larger the mass and the closer you are, the stronger the tidal force. When the object approaches a black hole, the tidal forces become so strong that they can tear the object. Spaghetti is where a black hole usually destroys an object, stretching its remains in a long stream. We have long suspected that stars break when they get too close to a black hole, and now astronomers have observed it in action.[^1]
This happened in the heart of a spiral galaxy just 215 million light-years from Earth. In September last year, astronomers saw a bright flash, which they called AT2019qiz. Observing it for about six months at wavelengths from the radio to the X-rays, they discovered that it was an event of tidal disorder (TDE). Almost half of the star’s material is consumed by the black hole, while the other half is ejected at a speed of nearly 10,000 kilometers per second.
This TDE is the closest such event to observation, and therefore gives us a much deeper understanding of how black holes can tear stars apart and engulf them. One surprise is that the black hole emits jets of matter as the star is consumed. These jets produce various optical and radio light emissions. Astronomers have observed similar emissions in galaxies, but their origins have been the subject of controversy.
Black holes play a significant role in the evolution of galaxies, including the formation of new stars. Through this recent TDE, we are beginning to see how black holes can simultaneously destroy stars and populate the galaxy with new material.
Reference: Nicholl, M., et al. “The eruption feeds the optical rise of the near-fast-growing tidal event AT2019qiz.” Monthly notices of the Royal Astronomical Society 499.1 (2020): 482.