A tidal shock occurs when a star cluster or other distributed astronomical object passes by a large mass such as an

interstellar cloud An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, the matter and radiation that exists in ...

, resulting in

gravitational perturbation In astronomy, perturbation is the complex motion of a massive body subjected to forces other than the gravitational attraction of a single other massive body. The other forces can include a third (fourth, fifth, etc.) body, resistance, as from ...

on a time scale that is much less than the mean time for a star to complete an orbit within the cluster. The

tidal force The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...

from this event can increase the dynamic energy of the cluster, in effect heating it up. This causes the cluster to expand and shed some of the outer stars. Tidal shocks occur, for example, when a

globular cluster A globular cluster is a spheroidal conglomeration of stars. Globular clusters are bound together by gravity, with a higher concentration of stars towards their centers. They can contain anywhere from tens of thousands to many millions of membe ...

passes through the galactic plane or near the core of the

Milky Way The Milky Way is the galaxy that includes our Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. ...

. These events are an important factor during the early evolution of a globular cluster. They work to truncate the outer part of clusters, thereby limiting the impact of future tidal shocks. Streams of stars shed from a globular cluster as a result of tidal shock can form what are termed tidal tails. These are extended streams of stars that lead away from the cluster. Such streams can be used to trace the orbital path of the cluster.

References

{{reflist, refs= {{cite journal , author=Ostriker, Jeremiah P. , author2=Spitzer, Lyman, Jr. , author3=Chevalier, Roger A. , title=On the Evolution of Globular Clusters , journal=

Astrophysical Journal ''The Astrophysical Journal'', often abbreviated ''ApJ'' (pronounced "ap jay") in references and speech, is a peer-reviewed scientific journal of astrophysics and astronomy, established in 1895 by American astronomers George Ellery Hale and ...

, volume=176 , page=L51 , date=September 1972 , doi=10.1086/181018 , bibcode=1972ApJ...176L..51O {{cite conference , author=Lee, Hyung Mok , title=The Life and Death of Globular Clusters , book-title=Extragalactic Star Clusters, IAU Symposium 207 , location=Pucon, Chile , date=March 12–16, 2001 , editor=D. Geisler , editor2=E.K. Grebel , editor3=D. Minniti , publication-place=San Francisco , publisher= Astronomical Society of the Pacific , publication-date=2002 , bibcode=2002IAUS..207..584L {{cite journal , title=The tidal tails of globular cluster Palomar 5 based on the neural networks method , author=Zou, Hu , author2=Wu, Zhen-Yu , author3=Ma, Jun , author4=Zhou, Xu , journal=Research in Astronomy and Astrophysics , volume=9 , issue=10 , pages=1131–1148 , date=October 2009 , doi=10.1088/1674-4527/9/10/005 , bibcode=2009RAA.....9.1131Z , arxiv = 0905.3614 , s2cid=8534666 {{cite journal , author=Yim, Ki-Jeong , author2=Lee, Hyung Mok , title=Tidal Tails of Globular Clusters , journal=Journal of the Korean Astronomical Society , volume=35 , issue=2 , pages=75–85 , date=June 2002 , bibcode=2002JKAS...35...75Y , doi = 10.5303/jkas.2002.35.2.075, doi-access=free Globular clusters Celestial mechanics