Add Boston Celtics co-owner Steve Pagliuca to the growing list of candidates vying for Massachusetts' vacant Senate seat.

The basketball giant, armed with millions in personal wealth, is expected to announce his candidacy on Thursday afternoon, according to local media. He will enter the field as a Democrat -- a move that pits him against Attorney General Martha Coakley, who has already declared her bid, and Rep. Michael Capuano (D-Mass.), who many expect to officially enter the race on Friday. A fourth Democratic challenger, Alan Khazei, is also mulling a campaign.

Pagliuca has already enlisted the help of a number of experienced political hands -- including Gov. Deval Patrick's (D) former chief of staff. He has also told reporters he plans to debut a number of advertisements introducing himself to voters within hours of entering the race.

Pagliuca is somewhat of a political neophyte, but he has one advantage over the rest of the Democratic field: no less than $400 million of his own money to spend on the campaign. However, sources close to the prospective candidate would not say how much of it he plans to devote to the special election.

The downside: The Celtics co-owner's bid for the Senate seat does mean he has to drop his bid for The Boston Globe.