Nova

A nova (plural novae or novas) or clessical nova (CN, plural CNe) is a transient astronomical event that causes the sudden appearance o a bricht, apparently "new" starn, that slawly fades ower several weeks or mony months. Novae involve an interaction atween twa starns that cause the flareup that is perceived as a new entity that is muckle brichter nor the stars involved.

Causes o the dramatic appearance o a nova vary, dependin on the circumstances o the twa progenitor stars. Aw observed novae involve closely locatit binar starns (the progenitors), aither a pair o reid dwarfs in the process o mergin, or a white dwarf an anither starn.

The main sub-clesses o novae are clessical novae, recurrent novae (RNe), an dwarf novae. Thay are aw conseedert tae be cataclysmic variable starns. Luminous reid novae share the name an are an aw cataclysmic variables, but are a different teep o event caused bi a stellar merger. An aw wi seemilar names are the muckle mair energetic supernovae (SNe) an kilonovae.

Clessical nova eruptions are the maist common teep o nova. Thay are likely creatit in a close binar starn seestem consistin o a white dwarf an aither a main sequence, sub-giant, or reid giant starn. Whan the orbital period faws in the range o several days tae ane day, the white dwarf is close eneuch tae its companion starn tae start drawin accretit matter ontae the surface o the white dwarf, that creates a dense but shallae atmosphere. This atmosphere is maistly hydrogen an is thermally heatit bi the het white dwarf, that eventually reaches a creetical temperatur causin rapid runawa igneetion bi fusion.

Frae the dramatic an sudden energies creatit, the nou hydrogen-birnt atmosphere is then dramatically expelled intil interstellar space, an its brichtened envelope is seen as the veesible licht creatit frae the nova event, an wis afore mistaen as a "new" starn. A few novae produce short-leeved nova remnants, lastin for meyhaps several centuries. Recurrent nova processes are the same as the clessical nova, except that the fusion igneetion mey be repetitive acause the companion starn can again feed the dense atmosphere o the white dwarf.

Novae maist eften occur in the sky alang the path o the Milky Wey, especially near the observed galactic centre in Sagittarius; houiver, they can appear onywhaur in the sky. Thay occur far mair frequent nor galactic supernovae, averagin aboot ten per year. Maist are fand telescopically, aiblins anerly ane ivery year tae aichteen months reachin nakit-ee veesibility. Novae reachin first or seicont magnitude occur anerly several times per century. The last bricht nova wis V1369 Centauri reaching 3.3 magnitude on 14 December 2013.