Be star Be stars are stars of spectral type B that have atypical spectra, suggesting the presence of a disc of material around the star at the location of its equator. The material is thought to be ejected from the star's atmosphere by its rotation, which is very rapid. In the Milky Way galaxy one in five B-type stars are observed to be of the Be class. Why some B stars become Be stars is unknown.
Big Bang The Big Bang theory describes how the Universe emerged from a dense, hot state in a single giant explosion (a 'big bang'). The principle of the theory was first suggested as an explanation for the fact that the Universe appears to be expanding. The Cosmic Microwave Background Radiation that fills the entire Universe is thought to be the remaining energy from the explosion. While other theories about the origins of the Universe do exist, the Big Bang theory is the most widely supported by models and observations.
Big Bang Nucleosynthesis Big Bang nucleosynthesis refers to the production of nuclei other than those of 1H (i.e. the normal, light isotope of hydrogen, whose nucleus consists of a single proton) during the early phases of the universe.
Binary star Two stars that orbit around a common centre of gravity are called binary or double stars. At least half of all stars are in a pair. Systems containing more than two stars have also been observed.
Black hole A black hole is a massive object or region in space that is so dense that within a certain radius, known as the event horizon, its gravitational force is so strong that not even light can escape from it. Although from their very nature black holes do not emit radiation for us to detect, material falling towards them can emit large amounts of energy. They can form either from the death of very massive stars following a supernova explosion, or from the collapse of large amounts of gas in the centre of galaxies.
Blazar A blazar is a type of active galaxy, with the central region emitting huge amounts of energy thought to be powered by a supermassive black hole. Typical for blazars is the variability of the energy they emit. Blazars are thought to be among the most energetic objects in the Universe.
Blue giant star Blue giants are stars weighing the equivalent of at least ten Suns. Usually of spectral type O or B, they are very hot and luminous, giving them a distinct 'blue' colour. Contrary to the regular use of the term giant star, they are not necessarily reaching the final stages of their life; the term 'giant' in this case was merely coined to indicate their extreme luminosity. The biggest blue giants are also referred to as supergiants.
Brown dwarf Brown dwarfs are gaseous objects that form like stars but lack the necessary mass to sustain nuclear fusion in their core. Their mass is typically in the range between the masses of stars and planets. Brown dwarfs are not very luminous and continue to cool down and contract until they turn into compact dark objects that are not easily detected. They can be seen orbiting other stars or free-floating in space.
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You can manage your cookie preferences and find out more by visiting 'Cookie Settings and Policy'.
ESO Cookies Policy
The European Organisation for Astronomical Research in the Southern Hemisphere (ESO) is the pre-eminent intergovernmental science and technology organisation in astronomy. It carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities for astronomy.
This Cookies Policy is intended to provide clarity by outlining the cookies used on the ESO public websites, their functions, the options you have for controlling them, and the ways you can contact us for additional details.
What are cookies?
Cookies are small pieces of data stored on your device by websites you visit. They serve various purposes, such as remembering login credentials and preferences and enhance your browsing experience.
Categories of cookies we use
Essential cookies (always active): These cookies are strictly necessary for the proper functioning of our website. Without these cookies, the website cannot operate correctly, and certain services, such as logging in or accessing secure areas, may not be available; because they are essential for the website’s operation, they cannot be disabled.
Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
csrftoken
XSRF protection token. We use this cookie to protect against cross-site request forgery attacks.
1st party
Stored
1 year
user_privacy
Your privacy choices. We use this cookie to save your privacy preferences.
1st party
Stored
6 months
_grecaptcha
We use reCAPTCHA to protect our forms against spam and abuse. reCAPTCHA sets a necessary cookie when executed for the purpose of providing its risk analysis. We use www.recaptcha.net instead of www.google.com in order to avoid unnecessary cookies from Google.
3rd party
Stored
6 months
Functional Cookies: These cookies enhance your browsing experience by enabling additional features and personalization, such as remembering your preferences and settings. While not strictly necessary for the website to function, they improve usability and convenience; these cookies are only placed if you provide your consent.
Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
Settings
preferred_language
Language settings. We use this cookie to remember your preferred language settings.
1st party
Stored
1 year
ON | OFF
sessionid
ESO Shop. We use this cookie to store your session information on the ESO Shop. This is just an identifier which is used on the server in order to allow you to purchase items in our shop.
1st party
Stored
2 weeks
ON | OFF
Analytics cookies: These cookies collect information about how visitors interact with our website, such as which pages are visited most often and how users navigate the site. This data helps us improve website performance, optimize content, and enhance the user experience; these cookies are only placed if you provide your consent. We use the following analytics cookies.
Matomo Cookies:
This website uses Matomo (formerly Piwik), an open source software which enables the statistical analysis of website visits. Matomo uses cookies (text files) which are saved on your computer and which allow us to analyze how you use our website. The website user information generated by the cookies will only be saved on the servers of our IT Department. We use this information to analyze www.eso.org visits and to prepare reports on website activities. These data will not be disclosed to third parties.
On behalf of ESO, Matomo will use this information for the purpose of evaluating your use of the website, compiling reports on website activity and providing other services relating to website activity and internet usage.
ON | OFF
Matomo cookies settings:
Cookie ID/Name
Description/Purpose
Provider (1st party or 3rd party)
Browser session cookie or Stored cookie?
Duration
Settings
_pk_id
Stores a unique visitor ID.
1st party
Stored
13 months
_pk_ses
Session cookie temporarily stores data for the visit.
1st party
Stored
30 minutes
_pk_ref
Stores attribution information (the referrer that brought the visitor to the website).
1st party
Stored
6 months
_pk_testcookie
Temporary cookie to check if a visitor’s browser supports cookies (set in Internet Explorer only).
1st party
Stored
Temporary cookie that expires almost immediately after being set.
Additional Third-party cookies on ESO websites: some of our pages display content from external providers, e.g. YouTube.
Such third-party services are outside of ESO control and may, at any time, change their terms of service, use of cookies, etc.
YouTube: Some videos on the ESO website are embedded from ESO’s official YouTube channel. We have enabled YouTube’s privacy-enhanced mode, meaning that no cookies are set unless the user actively clicks on the video to play it. Additionally, in this mode, YouTube does not store any personally identifiable cookie data for embedded video playbacks. For more details, please refer to YouTube’s embedding videos information page.
Cookies can also be classified based on the following elements.
Regarding the domain, there are:
First-party cookies, set by the website you are currently visiting. They are stored by the same domain that you are browsing and are used to enhance your experience on that site;
Third-party cookies, set by a domain other than the one you are currently visiting.
As for their duration, cookies can be:
Browser-session cookies, which are deleted when the user closes the browser;
Stored cookies, which stay on the user's device for a predetermined period of time.
How to manage cookies
Cookie settings: You can modify your cookie choices for the ESO webpages at any time by clicking on the link Cookie settings at the bottom of any page.
In your browser: If you wish to delete cookies or instruct your browser to delete or block cookies by default, please visit the help pages of your browser:
Please be aware that if you delete or decline cookies, certain functionalities of our website may be not be available and your browsing experience may be affected.
You can set most browsers to prevent any cookies being placed on your device, but you may then have to manually adjust some preferences every time you visit a site/page. And some services and functionalities may not work properly at all (e.g. profile logging-in, shop check out).
Updates to the ESO Cookies Policy
The ESO Cookies Policy may be subject to future updates, which will be made available on this page.
Additional information
For any queries related to cookies, please contact: pdprATesoDOTorg.
As ESO public webpages are managed by our Department of Communication, your questions will be dealt with the support of the said Department.